Playing a Warlock in an instance can be challenging the fist time. This is mainly because of the ability for a Warlock to accidently wipe a group with fear or not knowing about how many soul stones you’ll need.
What follows is a list of tips that are very helpful to understand before you head into an instance.

Not all of these tips apply at all times (especially during boss encounters), but in general they are a very good list of things to be aware of before you set off into an instance.

• You never know how many Soul Shards you’ll need to start with. Always assume you’ll need to hand out 5 health stones at the start, summon a pet, and have a few extra to work with. It’s usually a good idea to go in with at the very least 10-15 for a 5-man instance. Larger instances are much more demanding at the start and there are usually less enemies to get shards from. In those cases it is best to stock up as many as possible.
• Never fear an enemy unless you absolutely have to. Fear in instances outside of tactics for beating an encounter generally lead into a wipe. What happens is that the enemy will run ahead and grab a few more friends who will then come and wipe your group. Some encounters require fear, but in these cases your group will generally discuss it with you beforehand.
• Be ready to hand out Healthstones at the start and during the game. Be sure to have soul shards set aside to give Healthstones to any melee. They are on a separate timer then potions and are valuable in many encounters. This is why you should stock up on the start.
• Always try to drain the soul of an enemy if you have inventory space. Soul Shards can always be deleted for room and you never know when you’ll have a rush on Healthstones or come to a boss who you wipe on and have to use a few to set yourself back up.
• Direct damage is usually very bad, especially early on. Always try to (outside of encounters that require different tactics) to lead in with your DoT spells and let the main tank get aggro. As he’s working away at the enemy you can start expanding into more damage dealing spells. Your goal isn’t to nuke enemies down as fast as possible but instead maintain constant damage. Some Warlocks who spec differently may have different tactics, but always remember to let your tank get the enemies attention before trying for the major damage.
• Use Rank 1 Curse of Recklessness on Humanoid enemies to keep them from running away. Other spells like Drain Soul are also very mana efficient at their Rank 1 level. Rank 1 Corruption can be placed on multiple enemies with little to no worry about them aggroing you and they will all trigger Nightfall!
• Watch out and never DoT something that will be sheeped. If you know that something is going to be sheeped do not try to DoT it.
• Use the right curse at the right time. Curse of Agony is good for damage, Curse of Doom is great on enemies who will be alive for longer then a minute. Curse of Elements is great when you have a Mage in the group. Exhaustion is rarely useful in instances. Curse of Recklessness (Rank 1) will keep enemies from running way (most Humanoids flee when their health is at 15%) which is VERY useful in instances. Higher ranks are good if your group is alright with it, the more damage the enemies does is offset by how much armor it looses. Generally you’d want a lot of melee before you use Curse of Recklessness a lot. Curse of Shadow is good for multiple Warlocks and Shadow Priests. Curse of Tongues is great against casters. Curse of Weakness is good on multiple enemies attacking one target.
• Watch your pet and make sure they don’t wander off and aggro anything. Be sure to use the right pet at the right times. For instance, the Succubus is great when fighting Humanoids in order to keep on occupied with its charm ability. The Felguard is a great offtank and the Voidwalker is an alright offtank. The Imp is useful whenever you don’t need to charm enemies and just want something that’s cheap, stays alive often, and helps your entire group. The Felhunter is so-so in Instances; although encounters with a lot of debuffs it can be a real asset.
• Keep someone who can resurrect with a Soul Stone as much as possible. Priests and Paladins have a resurrect ability. Shamans can resurrect as well, but more then often their self-resurrect ability is up.
• Life Tap sparingly in the middle of the battle. Many healers will get VERY upset if it’s a close battle and you are using Life Tap causing them to waste their mana on you. There are situations where you have to, but generally it’s best to work out a way to Life Tap and not annoy your healers. Never Life Tap with an enemy on you or below 50% health.