I disagree with a few things in Lathais' build, but just my personal preference.
I'd be more inclined to go all the way to Shadow Mastery:
http://www.wowhead.com/?talent=Iq0riRbkq
Perks of this build:
- 1/5 Suppression effectively hit caps you since there's no +hit gear at your level
- 2/2 Improved Life Tap helps your mana efficiency loads
- 2/2 Improved Curse of Agony to eke out that extra damage wherever possible
- 5/5 Shadow Mastery, for the same reason
- 5/5 Fel Concentration to reduce pushback, though it should be noted that 3 points is all that's really needed
- Curse of Exhaustion, because kiting is fun
- 1/5 Shadow Embrace, for marginal benefit, and also dispel protection for your dots
Downsides:
- No Demonic Embrace
- No Improved Healthstone
http://www.wowhead.com/?talent=IZZVx0trhuh for a Destro build.
Perks:
- 5/5 Cataclysm for mana efficiency (though some would argue ISB is better)
- 5/5 Bane because warlock nukes are long casts, and instants are few and far between
- 2/2 Intensity for the above reason
- 5/5 Devastation, mostly to get to Ruin, but more crits means more damage
- 2/2 Destructive Reach to be nuking as far away as possible
- Ruin, because it is win
- Shadowburn, because it's an instant DD spell
- 3/3 Imp. Searing Pain because this will likely be your "main" nuke
- 3/5 Imp. Immolate for filler
- 3/3 Nether Protection, because it is awesome
Downsides:
- No Demonic Embrace/Imp. Healthstone
- Corruption is a cast time spell
Generally, it's widely agreed that Empowered Corruption isn't particularly useful unless you have a decent amount of spell damage. Also, 39 isn't the greatest bracket for warlocks; instead, the 49 bracket is a little better. Death Coil, Howl of Terror as trained spells, Dark Pact and Contagion if Affliction, Soul Link if Demo, Conflag if Destro, etc., and both Demo and Destro can pick up Imp. Corruption more effectively.
Obviously, much of this will change, come new xpac.