Casting basics
Being a pure caster can be a difficult role to play. Melee fighters rely on auto attacks to cause their damage and add on with activated abilities. But mages have no auto attacks and have to activate all of their damage dealing abilities. This means your ability to be an effective damage dealer will depend on your ability to cast as quickly and efficiently as possible.
Casting is actually a very straight forward process. While standing still, activate your spell and after you have charged it up you'll release a damaging attack. The difficulty is dealing with the factors that will hinder your casting. The most important thing for a caster is distance between themselves and the target. You want to make sure that they can't get close to you or you will fall fast, but if they are to far away they will run out of range and your spell will fizzle. When soloing start at the maximum distance between the target and yourself before casting. If you are in a group your tank should be keeping the enemy in one place, so move up a little closer to about three fourths your max distance. In PVP distance is a double edged sword. If you deal too much damage and are far away they may try to run and you won't be able to catch up. In addition to running away an enemy may run behind an obstacle and stop your casting. This is mainly done in PVP, but it can also happen occasionally in PVE as well. If you can, check the area to see if there is anything that and enemy could run behind like buildings, trees or pillars.
Another difficulty casters must face is spell push back. The reason you want your enemy to be as far away as possible is that when they get in your face and start hitting you it

becomes very hard to cast. Every hit will push back the progress you have made on casting your spell and make your cast take longer to complete. The faster your opponent attacks the more spell pushback you'll experience, so dual wielding classes are especially dangerous. To get around this try to get talents like Burning Soul that give you a chance to ignore spell push back. There are also many items and set bonuses that can help with this as well as some others classes abilities like Concentration Aura.
Damage dealing
A mages primary function is to be a hard damage dealer. How you go about doing that though depends largely on what talent spec you choose. Being a good DPSer is not about throwing all sorts of spells at random. A good DPSer will have a spell rotation where they cast spells in a certain order based on the kind of fight they are in and the cool downs of their abilities. Mage damage can come from three sources. Arcane, fire and frost. Each one of these styles is enhanced by their different talent trees and will have very different techniques.
Arcane
An Arcane mage can deal some of the largest amounts of damage in the game, but it only has three DPS spells and very little survivability. In my personal opinion I believe the arcane tree and spells are supposed to be support for fire and frost builds, but it is possible to be an arcane specialist. An arcane mage can come in two different flavors. The first uses arcane missiles and arcane blast for its core DPS. Every few seconds it will throw in a fire blast for extra DPS, a frost nova if the enemy gets to close or a pyroblast to open. You will get the most DPS as an arcane mage from using arcane blast. But this runs through a great deal of mana very quickly. If the fight is going to be a long one it is better to use arcane missiles more often and only use arcane blast when you get a clearcasting proc. If you are trying to burst an enemy down though arcane blast is usually better. Another factor is your total spell damage. If you have a very large amount, arcane missiles is better because its coefficient is nearly twice that of arcane blast. This type of mage is really rather limited and requires very good gear so I would not recommend it for beginners. On the plus side, you have some of the highest burst damage in the game which makes it very good for one on one fights.

The second type of arcane mage uses the arcane tree for support and will specialize in either fire or frost attacks. They may use an arcane missile occasionally when clear casting procs, but they will still be using frostbolt and fireball for the main DPS. The bottom portion of the arcane tree has several talents that drastically increase your spell damage and critical strikes, but leave few talents for the frost and fire trees. You won't get any of their low tiered abilities and will usually get stuck casting fireball and frost bolt. Since you aren't really using arcane spells to dps, I'll discuss arcane/fire and arcane/frost builds in their respective sections.
Fire
A fire mage is one of the best DPSers in the game. They have some solid burst damage, but specialize in sustainable damage. Because of this they are generally considered the best spec to go when doing PVE activities.
A full fire mage depends on hard steady attacks to deal damage. While crits are important a full fire mage tries to increase the base damage of their fire spells first. This is more effective in long fights like raids because when you crit your ignite spell will gain a larger bonus. Their main attack is their fireball, but before they start using it they use some of their other abilities first. Most fights should start with a Scorch or two to make the enemy vulnerable to fire damage. If you are in a group with several other fire mages you can each only cast it a few times to max out the debuff. After it is applied you will focus on chain casting fireball. This will be your main spell in long fights because it is very mana efficient. If you are safe in terms of threat try to use Combustion early on so you can use it again more quickly. If the fight starts to get too long and you are getting low on mana switch back to Scorch for a bit because of its low mana cost. Once you have a chance to regain some mana through a gem, consumable or Master of Elements proc switch back to fireball. If the fight will not take very long use your Fireblast whenever the cooldown is up and you aren't casting. It is not very mana efficient, but deals a quick burst of damage to spike up your DPS.

An arcane/fire build is focused less on sustainability and more on burst damage. This build focuses on big and frequent crits, with the cornerstone being the combination of presence of mind and pyroblast to give you an instant powerful attack. You will usually use this build in one on one fights in PVP where your opponent has to go down fast. If possible open with a regular pyroblast or polymorph your opponent and use a

regular one. After that use presence of mind and pyroblast again to finish them off. You can also use arcane power to increase your DPS during this time if you have plenty of mana and won't need it for later. If they aren't dead by then try to snare them with a frost spell and blink away to finish them off with a fireball. Your regular attacks will not hit for as much so spells like Scorch are not very worthwhile unless you know the fight will be long. Mana efficiency is also something of a problem so use your most mana intensive spells like arcane missiles when Arcane Concentration procs.
Frost
Frost is generally the lowest of the three builds when it comes to damage output. It makes up for it with the most control of the builds. A frost mage specializes in slowing their opponents movement with chill effects, or freezing them in place. If you do it correctly they will rarely ever get close enough to attack you, and if they do you have several defensive spells like Ice barrier to protect you.
Playing as a full frost mage has three different steps. Start as far away as you can and use frost bolt to damage and chill them. As they get closer continue to use frost bolt until they are either frozen or get too close. If they are frozen either back up and blink away, or stand and fire another frost bolt if they are low on health for the extra crit chance. If they don't become frozen or use an ability to get close like intercept use cone of cold when they are within range and blink away, or frost nova to freeze them and run.. Back up and start the process over again. This is known as frost kiting and it is very effective in PVP and solo PVE. If they are proving very tough or get close before your cool downs are up use your water elemental for extra DPS and its frost nova ability.
If you are trying to PVE as a full frost mage in a group or raid you will not be able to rely on freeze effects for your damage and you will be too far away for your instant casts to be of any use. Instead, use ice lance once or twice to get the winters chill debuff on your target and start spaming frost bolt.
An Arcane/Frost build is complicated and lacks much of the frost trees survivability, but is useful in large scale PVE activities. Your only frost spell of any use will be frost bolt since the others are AoE or require freeze effects to be useful. A bonus for arcane frost is the incredible crits you can achieve thanks to a combination of the spell power and ice shards talents. The raw damage of the arcane tree is also helpful because frost attacks are purposefully weaker than fire or

arcane. Playing as an arcane/frost mage is similar to a full frost mage since you will be relying on chill and freeze effects to slow your opponent. You won't have useful talents like winter's chill or ice barrier, but you will have presence of mind which will let you instantly cast a frost bolt if one of your attacks is resisted or your enemy gets to close.
Elementist
One last style of play is the elementist who combines frost and fire attacks. An elementist will still usually focus on either the frost or fire tree, but will mix in attacks from the other school as it suits them. A primarily fire mage can start fights with a pyroblast, then use a rank one frostbolt to slow the enemy down before casting fireball. If an enemy gets too close they can fall back on the survivability of frost with frost nova or ice block. A primarily frost mage can sometimes use fire as well. Pyroblast is a great opening move, though sometimes the dot portion will break a freeze. Fire blast becomes more powerful and has a shorter recast time. And if the enemy gets in your face and your cool downs aren't up you can use a blastwave to stun them while you get out of range.
Bursting
At certain times you will need to go above and beyond your normal damage. At certain points during a boss fight or when fighting in PVP your enemy will be especially vulnerable to damage and you need to make the most of it. Use abilities like combustion or arcane power and any trinkets that can be activated to boost your spells. Use your highest DPS spells like arcane missile, even if they suck up a lot of mana. Also try to save some of your abilities that have a cool down like fireblast, water elemental or presence of mind for these moments. It is important to watch your casting time though. Avoid super long casts like pyroblast because in the time it takes you to cast, you could have cast two fire balls with a chance to crit.
Supporting

Mages are mostly about damage dealing, but they do have a few abilities that help groups out. When it comes to buffing other players we only have two spells. Arcane intellect is a useful buff for casters, but when in a group use Arcane Brilliance to save time and mana. Our other buffs are amplify and dampen magic. These are some what tricky. Amplify magic will increase the amount of healing a target will get, but also increase the magical damage they take as well. Because of this it is best used in fights where there is no

chance of magic damage. Dampen magic does the reverse by reducing the among of damage taken from magical attacks, but also reducing the amount of healing a target will get. Groups rarely use dampen magic because of the reduced healing, but it can be useful when you are soloing since you won't have any healing.
Another unique ability of mage support is our ability to conjure water and food. Once you are together with your group mates conjure up food and water and give it out appropriately. If you are level seventy, wait for everyone to gather together and put down a refreshment table to save time.
One support ability that you will be occasionally called upon to do in a battle is de-curse an ally. Since you are a DPSer and not a supporter if possible have a druid remove the curse. But if there isn't one available shift your focus to de-curse your allies. Tanks and healers get top priority and then yourself and any other DPS. If the curse doesn't have a dangerous effect like reducing attack power or lowering damage it isn't a high priority and you can finish what you are doing before de-cursing. But if it has a negative effect like increasing damage by a certain school or dealing a large amount of damage over time focus on clearing it right away.

The best support a mage can bring to a group though is our crowd control. When fighting multiple mobs you can take one completely out of the picture by Polymorphing it. To do it successfully try to cast as soon as the puller has pulled the group and the target is in range. This way it will be away from your tank and won't be released with AOE attacks. The key to being a good Ccer is knowing when to reapply the spell. Use a spell timer addon to see when it is about to break free and use a focus polymorph macro so you don't have to switch targets. (This is in the macro section.) It is also important to know which targets to CC. If the group has three heavy damage dealers you will want to CC the most dangerous. If any of them have nasty abilities like a fear or silence it is good to CC them first so you can all focus on him later. Some people like to CC the healer in the group to prevent them from healing their allies, but I've found that healers drop fast and it is easier to fight a healer and DPSer than two DPSers.

Mana management
One of the more challenging aspects of playing as a mage is making sure you don't run out of mana. After all, you can't go BOOM if you are always OOM. Mana regeneration comes in three different forms. The first is through abilities. The only mage ability that instantly returns mana is Evocation. Because its cooldown is so long it is best to use it as often as possible when leveling, grinding or in PVP. If you are in a group though try to save it for very long fights, especially bosses. Besides evocate there are several talents that help you regain mana and are considered necessary for most serious mages. Arcane Concentration will roughly make every tenth spell cost no mana and Arcane Meditation will help your base mana regeneration. Besides those there are different talents in the frost and fire trees that reduce the amount of mana your spells cost directly, and other talents like Master of Elements will give you back mana when you make a critical strike.
The second way to manage mana is through gear. The basic way of doing this is through spirit, but there are some problems with this. The primary culprit is that mages are hindered by the five second rule. Spirit based mana regeneration stops when you start casting a spell, and won't pick up until five seconds later. If you are trying to Dps you will be casting nearly every second and you will rarely get past the five second rule. The only way to get around this is through talents like Arcane Meditation and spells like Mage Armor that allow your spirit based regeneration to continue even when casting. The other way of regenerating mana is through mana per five gear. This works like spirit by returning a set amount of mana to you every five seconds, but isn't effected by casting. Mana per five gear with good damage dealing stats is somewhat rare, but is preferable to wasting time with spirit.

The final way of managing your mana is through consumables. You should always try to have a large stack of mana potions on hand. Since these cost money it is better to save them as a last resort when you are at 15% percent of your mana and the fight will still go on for a while. In addition to mana potions, always keep several mana gems available. If you are fighting alone keep them on hand for an emergency and use the highest level one. If you are in a raid or a long fight use one whenever their cool down is up. It is best in this case to use the lower level ones first and use a higher level one as you go along. Otherwise you might gain more mana than you need and waste it.

Threat management
When soloing, a monster has no choice but to focus on you during a battle. But when you are fighting as a group the enemy fights the target it feels is the biggest threat. Tanks have abilities that make them seem like the biggest threat, but if a character does too much damage too fast or heals away all the monsters damage it will ignore the tank and focus on the other player. Since it is hard to constantly keep track of your damage if you are going to do any group play you should have a threat meter addon. These will show each of the party members threat and advise you when to back off.
Dealing with threat as a mage comes down to two forms. The first is managing your threat by controlling your damage. A tank is able to create threat at a much higher rate than you, but it takes them some time. When a fight first starts don't go crazy and use powerful nukes like pyroblast or arcane missiles. Use two or three scorches first if you are fire speced before using your fire ball. If you are frost specced cast frost bolt but pause a second or two before casting again. After about ten seconds the tank should have gained enough threat for you to DPS safely. You should also invest in talents that reduce your threat like burning soul and frost channeling and any enchants that reduce your threat.
Even if you are careful you will occasionally gain more threat than is safe. At these times you need to shed yourself of some of that threat. The simplest way is to stop dpsing, but this is inefficient since you won't be helping. Instead try to reduce your threat by using Invisibility. Every tic of invisibility will reduce your threat by 10% until you are completely invisible and it resets it to zero. Reseting your threat to zero is especially nice for boss battles so you can come back out and dps like mad. If you do manage to out threat the tank and the monster starts coming for you, you have very few options for reducing your threat. Your best bet is to use Ice Block to prevent any damage. This does not reset your threat, but since you are immune to any damage the enemy will go back to the tank and he will hopefully be able to regain control by the time you unfreeze.