Choosing a talent path...Follow

It's generally considered that Affliction is the more efficient leveling tree. Start with Improved Corruption, Improved Life Tap and Soul Siphon. At the earlier levels you'll be "drain-hunting" more than anything (using your pet as tank, as opposed to "drain-tanking" where you're the tank), so just send in the blueberry, dot up the mob and start to draining.

This method is also great for chain pulling. Once the first mob is pretty close to death you can send the blueberry after a new one as you finish off the first, rinse and repeat. I remember pulling my way through many a zone by chain pulling this way.

Good luck!

Affliction and demonology both have good survivability, affliction because you have a constant stream of health coming at you due to soul siphon and a beefed up drain life, and demonology due to the fact that your demon will be taking all the damage. Destruction lets you burn mobs down quicker than the other trees, but you lose survivability and you end up having to drink alot.

Any tree will be fine for leveling, it just depends on what you want to do. Do you want to drain tank and never run out of health or mana? Do you want your demon to tank for you and never run out of health or mana? Or do you want to burst crap down but have to drink?

I see your question was answered well , one tip i can give you, if you go for the drain tanking is be sure to get good stamina gear as that is all you really need and whatever other stats you get while levelling are just a bonus.

I went affliction and i found by using the succubus once i had got her and drain tanking i was on easy mode , and as the succubus is the highest damage pet at my level depending on what mobs i am fighting she is my preferred choice , apply dots drain repeat on next mob and the only times i die is by making stupid mistakes as if you set up with the right glyphs and talents you heal pretty good .

One tip for anyone that goes the drain route is get an addon like "shard" = easy mode control of shards instead of full bags , set number between 1-28 and forget about your bags being full of shards.

Hey, I can give hints, too.

Remember that Life Tap is your friend. I know that it seems silly (at least it did to me, when I was low level) to think that giving up health for any reason whatsoever. However, you get the health back when you Drain Life, so it's not so bad after all.

You will find that you have to use different tactics when you join a group to go through an instance. In that case, the mobs are dropping too fast for drain to give you much life, and you have to rely on the group's healer to give you back your health (alternative: lifetap until mana is full, and then bandage yourself).

Learn first aid, so that whenever you are low on mana, you can do the life Tap/bandage routine.