Be you a Warlock player, you may want to know the Warlock PvE guide badly need. Now we are willing to make mention of this topic in detail in order to make you clear of this information. The detailed content is as follows.
First of all, you do not Lifetap below 50% without telling your healer. We're often looking at your health bar and not at what you're doing and we don't like to throw a big heal at you if you're just going to bandage anyway. And a Warlock has one serious way to heal himself, lifedraining, with its telltale green line.
Even with 5/5 cataclysm a heavy runecloth bandage only gives about 7 shadowbolts, it's only a last resort way of regeneration. Healthstones might be good to suggest if the party goes to the limits of its ability but otherwise creating/using them isn't efficient. If a healer uses a mana potion, that is much more efficient than a Warlock using a healing or mana potion. If it's about who is paying, its best the Warlock pays manapotions to healers for heals.
Now it is time to talk about interpretation of the Warlock health. Of course, cases that everyone takes damage exist, which includes situations where nearly every DPS might need to offtank, and AoE exists, maybe a Warlock tanks a caster, but in all other situations a warlock shouldn't have aggro, nor take damage from mobs.
In part, a healer gets to know an encounter for the most part, he won't have doubts whether a responsible non-over-aggroing DOS might take damage or not. Exceptions like the main tank dieing are pretty obvious.
In such situations where damage to DPS is unlikely, a healer can assume that Warlock health is not be an emergency, even if he is at 1 HP, and always just means that a Warlock could use mana. Of course the Warlock typically has lower priority than tanks.
If Warlocks rely on life draining, optimal long fight behavior will include making sure that all draining is useful, that is, does heal, which means going fairly low. If healers are going to use heals able to crit, or more than one healer might consider healing, the best practice is to make sure all of the potentially healing will be useful, meaning going fairly low.
If the party is low on healing and relies on eating/drinking after fights, it is probably best for a warlock to keep mana/life distance to the max and both eat and drink after.
You do not expect your healer to be your mana battery along the same line. We're happy to drop you heal over time now and again, but asking us to burn our mana just to fuel yours is rude.
Demanding to be healed at once would be rude for a warlock but a life tap shouldn't be interpreted that way. It is just smart to enable the option to be helped with mana early.
There's a way for Warlock to ress if the healer dies and Soul-stone was on cool-down. Whether you can tell them to enter the entrance and ress or to ress at the graveyard if this is not possible or will take too long.