speccing a warlock is a very simple task. One thing depends on how you want to play the game. If ur a guy that like pumping shadowbolts into a creep, go destruction (recommended only for undead or large mana pool warlocks. If ur a guy who likes watching creeps suffer slowly, go affliction. If ur a guy who likes demons to do the job for you, go demonology.
For grinding, you need to be sure on what spells to cast and when to lifetap and drain life (Drain life is extremely helpful for going through long periods of time w/o eating/drinking/canabalizing). Count how long it takes the monster to die from you DoT (affliction) or how many shadowbolts/searing pains it takes to kill a monster. A very helpful addon is
MOBINFO2 which displays the health of the monster/player targetted. If possible,choose a place to grind where there are enough monsters to continuously grind w/o having to stop.
Spells: I have made many mistakes with grinding/lvling, and only when i hit 70 did i realize what spells are important.
if you have shadow dmg, dont bother casting anything but shadow spells (immolate). Likewise, if your destruction fire=fire spells, shadow=shadow spells. One curse that is really helpful is Curse of Shadows/Curse of Elements. If you go affliction, dont bother with curse of agony (too slow). Curse of Shadows buffs your shadow spells, so lets say you place a Corruption, Siphon life, UA, and CoS. Corruption, Siphon, UA, and Drain life all get (8%@44 10%@56 and Malediction +3% and reduces resistance to shadow so no worrying about spells resisted). Demonology it doesnt really matter which spells you cast, but if you drain tank, i strongly recommend using CoS for more health. Health funnel when demon is bellow 50%. Keep a good eye on your demons health and your health so that you don't end up in a situation where your both low on health.
For stats. Destro: intellect, stamina, and fire/shadow dmg. Affliction: stamina, shadow dmg. Demo: intellect, stamina.
I have assembled 3 trees for every specc. Hopefully they will help.
http://www.wowhead.com/?talent=IVMrMZbgIzhizcest http://www.wowhead.com/?talent=IVMrVMctVtcobgIzh http://www.wowhead.com/?talent=IZcxZVEbtr0tAuA In my opinion, Demonology is the best for lvling. I used demo 1-70 and never had any problems. Destruction is not recommended, but if your bored, you can always try new things.
One last thing, on one of the warlock quests, absolutely go for the trinket: Abyss Shard (over Soul Harvester or Robes). Robes and weapon and easily be replaced, but the trinket stays forever. No need for shard or mana for your voidwalker.
GL and HF on your warlock