Groups tend to have a tank (typically warrior, druid or paladin). The tank will try to make sure every enemy is hitting him instead of a more feeble class. You do not want to pull aggro away from the tank and onto you. This can create chaos on difficult fights, and often gets the healer killed. Consider using searing pain to pull an add of the healer if the tank doesn’t do that quickly. It can save a fight. While a warlock can take a fair beating utilizing lifestealing abilities, you still don’t normally want to pull aggro away from the tank. If you do want to handle an add when often too many are pulled at once, tell the group what you’re planning.
Now.. how to make sure you don’t steal aggro?
-Don’t hit the target with anything before the tank has hit the enemy.
-Wait a few seconds before you start casting spells when fighting tough enemies. It will help the tank keep aggro.
-Opening up with a shadowbolt or soulfire before the tank gets a few hits in is a bad idea.
-Don’t use searing pain if you can avoid it (and you can, most of the time). It causes much more aggro than shadow bolt or incinerate.
-Don’t move too far from the tank unless you are quite sure you will not be drawing aggro. Being far away will cause additional problems because the enemy will come running to you forcing every melee to move. It is better to be semi-close to the tank to limit chaos. Maintain a little distance though, you dont want to be in melee range of the target either.
-If you do get aggro, don’t start running in circles like a freak when you see your healthbar plummeting. Besides looking stupid, you are confusing everyone. By having friend and foe running in every direction, crowd control becomes much more difficult. Just stop, drop, and die. You’ll get rezzed later. Or, if you have it, use Soulshatter to ditch that aggro!
Curses

Curse of Recklessness can be extremely important in a group, especially in instances. You will generally want to cast this on every enemy that is likely to flee when low on

health. Rampant adds are the #1 reason for groups to get killed. Sometimes someone else can take care of the runners (like a rogue, by using their cripple poison on them, or a warrior with hamstring). You may want to discuss whether you or someone else will be taking care of preventing runners before you decide to stop casting recklessness.
Note that it isnt necessary to keep recklessness on a target the whole fight, you can switch to it when the target is getting low on health. Note that you can use rank 1 curse of recklessness to limit its negative side effect of increased damage from the target.
Curse of Weakness; If your tank keeps experiencing near-death, you can try casting curse of weakness first, and follow up with recklessness when enemies are about to run away. Using CoW against very hard hitting elites tends to have a very small effect and is often not worth it. Curse of Weakness causes a fair amount of aggro, so be aware of that when using it.
Curse of Tongues helps a good deal against casters. Sometimes the casters die so quickly that it’s not worth using the mana on CoT. You should be able to tell when that’s the case.
Curse of Elements and Curse of Shadow have their uses as well. Curse of Shadow helps when you are trying to banish or use enslave demon against a resistant enemy to help land the spell.
Curse of Agony can be of use against anything that takes a long time to kill. Dealing most of its damage at the end of its course, it is not well suited for killing regular enemies. Those generally die far too quickly for the curse to finish, unless you are fighting elites above your level and its taking long to kill them.
If you are level 60, you will have Curse of Doom. This one has to remain on the target for 1 minute, and then deals all its damage at once. Which is a lot, 3200. And for a measily 300 mana. It does more damage than curse of agony in that period, unless you have a large amount of spell damage. It has a 1 minute cooldown before it can be cast again, which also works as a timer. When the cooldown is almost up, you know the Curse of Doom you currently have on your target is going to go off. It does not work on PC’s, so has no use in PvP sadly. It has three main uses.

1.Tough enemies that take over a minute to kill. Beware aggro from the sudden 3200 damage going off though.
2.Weaken an add. If you are assigned to keep an add seduced, you can cast curse of doom on it. When it goes off, just seduce it again. Results may vary on sheeped adds. For one, mages don’t like their sheep getting broken unexpectedly much. For two, a sheeped enemy regenerates its health in no time, so its pointless to do unless you discuss it with the mage. (You could take over with seduce when sheep wears from the CoD damage.)
3.Most obviously, the chance to summon a Doomguard for use as pet. This can be more of a risk than a gain
Conjuring And Soulshards
First off, it is a good idea to dedicate one of your bags to soulshard storage until you get your hands on a shard bag. Using less than a bags space for shards works too, but it really stinks if you can’t provide a soulstone when the situation demands it.
Creating healthstones(min lvl 10) and using soulstones(min lvl 18) is something that will be expected of you in a group, similar to how people expect mages to summon food and water.
Some warlocks will gladly supply the group with an endless supply of healthstones and encourage everyone to use them whenever they lose some hp. I’ll usually ask who wants a stone when the group is formed, and will make sure the tank always has one.
Beyond level 68, you will have Ritual of Souls. This lets you provide the whole group with healthstones at the cost of one shard, which makes locks quite a bit more generous with their juicy green stones.
Soulstones are a different story, they can prevent group wipes. Some tips:
-Use the soulstone on a class that can resurrect. Paladin, Shaman, Priest, or a Druid. (Druids can only rez one target every 30 minutes, but its better then nothing) If there is no rezzing class in the group (it happens, especially at low levels) see if someone has a gnomish jumper cables.

-Make sure you have a soulstone in your inventory at all times. In case the group wipes, you will be able to recast soulstone on the rezzer immediately once the cooldown passes, and not be caught without a shard to cast a soulstone.
-Make sure the person with the stored soul tells you when the effect wears off. You can also keep tabs on this by casting demon skin on yourself right before you use soulstone on someone. Both spells have the same duration, so when Demon skin fades, you will know the soulstone effect is fading soon as well. A better option is to grab one of the addons that give you a cooldown timer, such as Dotimer, Shard Tracker or Necrosis.
Crowd Control
Besides utilizing the Succubus' seduce ability, you have banish at your disposal. Banish has a limited use in that it can only be used against demons and elementals. (Some of those will still be immune to it) If you do use it however, use it well. If you are to keep a demon under control with banish, recast it the moment it wears off. If the target is resisting it, you can use Curse of shadow to lower its resists. Keep in mind you can only keep one target banished at a time. Cast it on something else, and the first one will wear off immediately. Crowd control (or CC) is not limited to spells. You could consider using a pet to off-tank CC as well.
Fear
Generally speaking, if you aren’t absolutely sure that there are no other enemies nearby, never use fear in a group. If your group is having a really tough fight and you fear an enemy which then returns with two of his friends, then you’ve just decided the fight in a negative way. Fear is very risky, don’t use it in a group unless you know what you're doing.
With that said, fear can be a valuable asset in certain situations. As an example; In Blackrock Depths there is an event where you find yourself in a room with locked doors. The last enemy you need to kill spawns three voidwalker pets. They can safely be feared, and in case the fight was difficult, it can be a good help.
When to use fear comes down to your judgement. If you consider it safe, you might try it. But if you get adds from fear, expect to get yelled at.

Fear Pingpong
This is a little trick you can use to prevent feared mobs (or even players) from running away too far. If you cast Curse of Recklessness on a feared target, it will cease running away and come back to whoever it hates the most. If you now swap to a different curse, the target will run away again. You can keep doing this until fear wears off. You can of course re-apply fear and keep this going for as long as necessary. It is a very helpful tactic from time to time.
Area Of Effect Spells
Hellfire and Rain of Fire are in some cases required to dispose of groups of weaker enemies swiftly. AEs are generally used against larger amounts (more then 3) of non-elite enemies, elites have too much life and will turn their special attention to you (ie rip you apart) before you can get them dead. If you are going to use AE, let your group know in advance. Simply running in and starting can get you dead pretty quickly. If there is a mage in the group, he/she may be casting frost nova to keep the enemies rooted in place for a while. You can AE easily if you see them stuck in icy blocks. (unless you keep standing in melee range of them) You can make a voidwalker in advance and use sacrifice to live a little longer. The Intensity talent helps out a great deal if you find yourself AEing often. Pyroclasm looks good on paper, but the 13 / 26% chance it gives to stun is for the entire duration of the spell. This amounts to having a very small chance to actually stun anything, making the talent not worthwhile. At 70, you get seed of corruption, which has a huge benefit in causing very little aggro.. until it goes off. It is perfect for dealing with large crowds of low to medium hp monsters. Normally, you will want to cast seed on as many targets as possible before the first one goes off. They will be going off in short succession. If, after the explosions, your targets arent dead.. you can be sure to have their individed attention.
Pulling Casters

There are several ways to pull a caster. They tend to enjoy stopping to cast spells a lot, and when getting nearer to them is dangerous, they will need to be convinced to come running to the group. One way of doing this (it’s usually the tank that would do

this) is running out of their line of sight, behind a wall or somesuch. They wont be able to see their target, and will make their way over (reluctantly, stopping frequently).
Another way is to interrupt their spell. Mages and Shamans can do this, and we can use spell lock for it.
Pets
Deciding which pet to use in a group can be a tough choice. Things to consider are;
-Group composition (which classes and what levels?)
-What kind of enemies you’ll be fighting (humanoid?), and their level compared to yours.
-How many enemies you’ll be fighting at a time.
-Whether or not the people in your group are skilled players.
When grouping with people you don’t know, the last point in the list is something you will find out after starting, and may cause you to switch pets (or use your hearthstone) after you’ve been playing in that group for a while.
Imp – Group Tactics
Due to his Blood Pact aura and damage shield, the imp is liked in groups. The imp is mostly seen doing absolutely nothing but provide blood pact. A shame, because he can do some nice damage. Don’t be afraid (or too lazy) to use him when you can. They’re resummoned easily, but if they die too often it may be better to go with plan a and keep him just for the buff.
If your group is having trouble with large pulls, consider using succubus (when fighting humanoids), voidwalker or felguard to assist with crowd control.
Voidwalker – Group Tactics
With his tanking ability and taunts, the voidwalker can be used as an offtank to keep one or more enemies occupied while the rest of the group focuses on the main target. He can be very useful in instances with high risk of adds and/or large pulls.

If you have a mage in the group, be very wary that you do not have your pet attack a target that has just been polymorphed. On tough pulls it can be wise to have the puller assign a target or raid icon to mage and offtanks (including your pet) before pulling, so that crowd control doesn’t turn into a cesspool of frustration.
In some (rare) cases, you may have voidwalker or felguard as main tank. Make sure your healer(s) know that targeting your pet can be done using: Shift + F1 - F5 (# corresponds to party member)
Pay close attention to your pets' manabar. If he’s running out of mana constantly, you may want to turn take the taunt off autocast and go for manual casting (Don’t cast at the end of a fight and cast with greater intervals then the timer allows) to preserve mana.
Also, try to avoid casting suffering when it isn’t necessary, as it costs a lot of mana.
You wont really have mana issues when you have the Mana Feed talent.
If you’re going to heal your pet with consume shadows or health funnel, let the healer(s) know so they won’t waste their mana. If your healer(s) have mana to spare, you can also forego using consume shadows and ask the healers to take care of it.
Succubus – Group Tactics
The seduction ability is the main reason to use Succubus in groups. Being able to sleep(basically disable) humanoids can be a great help, especially when you’re dealing with large pulls or your group doesn’t have good CC to begin with. In the heat of battle, make sure you notice when seduction wears off so you don’t get her killed. If you see her taking hits, that’s usually a safe bet that seduction dropped and you need to recast. You can put seduction on autocast, but she will pick her own target to seduce in that case.
Succubus does decent melee damage, so even if crowd control is totally taken care of she counts as some extra dps.
When manoeuvring in tight spaces and avoiding aggro is important, the succubus’ invisibility will allow you to have a pet out and be confident you won’t kill your group if your pet takes a misstep. This goes for imp and his phase shift ablity too.

Felhunter – Group Tactics
Felhunters are good against casters, but since his hitpoints are considerably lower than that of the voidwalker, he will die too fast to be a decent offtank. He is not good at drawing aggro away from someone, so you won’t be saving your healer from an angry add that way. He may have his moments, but I can’t recommend him for use in a group unless you are fighting relatively easy non-elite enemies, or the enemies have a debuff or buff on themselves that felhunter can get rid of. He can also provide some help with the stealth detection aura in some instances, albeit very situational.
Felguard – Group Tactics
The felguard comes with a manual in groups. He makes for nice added damage, and can even perform as an offtank in none too difficult circumstances. There are two things that can cause confusion or downright problems. One, intercept. He will often intercept nearby mobs at random, ust because he can. He won't hit them, just intercept and then return to what he was fighting. If you dont want this to happen, take intercept off autocast. Cleave can be a troublemaker when it's breaking CC, so thats another one you may want to turn off. Lastly, if there is only one target to fight, a Felguard will frequently steal aggro from the tank. On bosses, this can mean a dead Felguard.
Otherwise, he makes for nice damage and can be quite a nice pet in instances.