Strength
The primary purpose of strength is to increase your melee damage. Each point will increase your attack power by two, which is then used to increase your green damage. However, since you have very poor melee abilities there is no point in getting strength.

Agility
Agility has three purposes which all directly impact the percentage system. The first and most important is that it increases your chance of getting a melee critical strike. The second use for agility is that it will increase your chance to dodge an attack. The final use for agility is that it increases your armor. Every point of agility will give you two extra armor.
This is another melee stat though so as a mage you should try to skip it. You may be tempted to get some for the extra dodge, but you need so much it just isn't worth it.
Stamina
Stamina is a very simple stat. For each point of stamina you have you will gain an extra ten HP. It may not seem like much but with thirteen equipment slots it will add up significantly. Since a mage has a hard time with survivability getting some extra stamina from gear is usually very handy. Getting armor with stamina alone though is not a good choice. In order to live up to your full potential as a damage dealer you will need a lot of spell crit, intellect and spell damage. This usually makes stamina a secondary priority, so instead try to get pieces that have stamina and another mage stat. How much stamina you ultimately need depends on what you will be doing. If you are playing in PVP it is a very high priority, otherwise you will get one shotted. If you plan to raid or do group play it is less important since you will have a tank taking the hits for you.
Intellect
Intellect is mainly used for casting and spells. Its first and primary purpose is to increase your mana pool. Every point of intellect will give you 15 extra MP. Much like stamina, it will increase dramatically if you spread it out over your equipment slots. It’s second purpose it to increase your chance to get a critical strike with spells. At level seventy you will need about 80 intellect for an extra 1% critical strike chance with spells. Intellect is the most important stat you can have as a mage because it is about the only way you can increase your mana pool. Some builds like Arcane use up mana very quickly and you will want to focus on it more than other mage stats. The extra critical strike chance is mostly a bonus and if you are going for a crit heavy build, use spell critical strike gear instead.
Spirit
Spirit is a complicated stat. Its only purpose is to increase your health and mana regeneration, but it will not do it regularly. Every two seconds or “tick” you will gain a

portion of your health or mana back depending on how much spirit you have. Health is one forth of your total spirit every two seconds. And mana is one forth your total mana with an extra eight tacked on. The tricky part is that whenever you cast a spell you mana regeneration is paused for five seconds. This is sometimes known as the five second rule and is a huge problem for casters. Mages should be casting every chance they get so you will have very little opportunity to get around the five second rule. Since mana regeneration is vital to a mage you need to find a way around it. The best solution is to try and find gear that returns a set amount of mana every five seconds. It isn't affected by casting so it will give you a steady stream of extra mana.
Attributes
Armor
The primary purpose of armor is to reduce the damage you take from physical attacks by a percentage. The formula for how much is reduced is (your armor/(your armor + ((85*level) + 400))). The formula is rather complicated but at level one, one hundred armor will reduce the damage you take by twenty percent. At level sixty, one hundred armor will reduce the damage you take by two percent. And at level seventy it will reduce the amount of damage you take by 1.79%. Since we can only wear cloth we have some of the lowest armor in the game. It is usually so low that I never even consider how much armor is on a piece of equipment when I use it. There are some cases where a mage might want to consider armor though. When used with Ice Armor and certain talents in the Arcane tree they can achieve some acceptable damage mitigation. But this gimps you so much that I wouldn't bother with it.
Defense

Defense is another stat used to reduce melee damage. One point will increase your chance to dodge, parry and block an attack with a shield by .04%. So you will need twenty five points in defense to get a 1% increase to your dodge, parry and block chance. Twenty five points will also reduce your enemies chance to hit, critically strike or deal a crushing blow by 1%. (beast version of critical strike.) You can probably see that while armor reduces the amount of damage you take, defense tries to prevent you from taking damage at all. The problem is that the amount of defense you will need in order to have a noticeable effect is very large and it means you will have to give up on other stats. Defense is primarily a stat for hardcore tanks anyway so as a mage don't worry about it.

Attack power
Attack power is the stat that determines your melee damage. Since a mage does not melee though this is unnecessary.
+Magic damage.
Magic damage is one of the best stats you can get in the game, especially in the end game. It takes the base damage from a spell you have cast and then adds a bonus onto it, making your spells more potent.
An important thing to remember about spell damage is that your spells will not get the full bonus. If you have one hundred extra spell damage, your spells will not get an extra one hundred points of damage. There are several factors like its casting time, damage over time, AOE and whether it is a channeled spell. Generally, the longer it takes to cast a spell the more of a bonus you will gain. But the shorter it takes to cast a spell, the less of a bonus it will get. A fireball gains 100% of your spell damage because it has a long cast time of 3.5 seconds (untalented). But Fire Blast only gets 43% percent because it is an instant cast. Here is a list of your most important spells and their spell damage percents.
Fireball-100%
Pyroblast-115%/DOT-20%
Scorch-42%
Fire Blast- 42%
Flamestrike- 18%/DOT-11%
Blast Wave-14%
Dragons Breath- 14%
Frostbolt-81%
Blizzard- 76%
Cone of Cold- 14%
Frost Nova-14%
Ice Lance- 14%
Ice Barrier-10%
Arcane Missiles- 143
Arcane Blast- 71%
Arcane Explosion- 22%
Magical resistances.

Magic resistance doesn’t come into effect until level sixty and beyond, then it is only necessary if you plan on doing raids. The main point of resistance is to reduce damage by elemental and magic attacks much like your armor and defense skill reduces physical damage. But instead of reducing by a set percentage, resistance gives you a chance to reduce a set percentage. Most players get their first taste of resistance when they go to the Molten Core so we will use that for an example. While in the core a Firelord hits you with a flame blast for one

hundred damage (In reality they hit for much MUCH harder but this is just to simplify things.) With zero fire resistance you will always take one hundred points of damage. But with a higher rating you will have a chance of reducing either 25%, 50%, 75%, or 100% of the damage you will take. Now let say that the fire lord hits you with his fire blast but you have 50 fire resist (A very small amount). This means that instead of a 100% chance of taking damage, you only have a 54% chance. Since this formula contains so many layers here is a table showing what you can expect for different levels of resistances.