For warlock players that want to be specc'ed groupbased for instances and also be good at pvp'ing I would suggest putting points in Tree Afflication and Destruction. Players that solo most of the time can look into the demonology tree.
My Tree:
1. Afflication Tree (24 points):
Supression - 5/5
Improve Curse of Weakness - 3/3
Improved Life Tap - 2/2
Fel Concentration - 5/5
Nightfall - 2/2
Improved Drain Mana - 1/2
Siphon Life - 1/1
You almost never get an interruption during channeling drain life/mana/soul.
The improved lifetap talent is a MUST ! Whenever a warlock falls out of mana all he can rely on is his lifetab and stamina pool.
A cool extra is Nightfall 2 points, then, on regular basis you can insta-cast a shadowbolt which adds to pvpcoolness and single-player gaming. Improved curse of weakness to protect group and self against npc's that hit realy hard, it's also usefull in pvp to weaken the warrior and rogue criticals.
PVP Coolness:
Grim Reach - 2/2
Amplify Curse - 1/1
Curse of exhaustion - 1/1
Improved Curse of Exhaustion - 1/4
Increase range of affliction spells is superfun for pvp, finaly you can start draining on that hunter that's standing on front lines
.
Curse of exhaustion combined with amplified Curse is now also very usefull in warsong gulch when alliance goes stealing our flag.
2. Destruction Tree (27 points):
For Maximum DMG:
Improved Shadowbolt - 5/5
Bane - 5/5
Devastation - 5/5
Improved Searing Pain - 5/5
Ruin - 1/1
Intensity - 2/2
PVP coolness and also must for instancing in my opinion
Pyroclasm - 2/2
Destructive Reach - 2/2
3. No points in Demonolgy.
Even with no points in Demonology you get the Sacrifice spell on the Voidwalker. As our last effort of protection, sacrifice , offers the voidwalker and puts a 30sec immune shield on the warlock which has safed my ass hundreds of times
Now, For modifiers on Armor, I think we should get at least 3 different sets and carry those with us all the time on our adventures.
1. stamina set
2. intellect set
3. spirit set
Keep in mind that it is difficult to get setpieces with only 1 modifier on it, most of the time a setpiece item contains more modifiers.
Now on use for these sets:
1. Stamina set: You would use the stamina set when you engage in a fight where you get quite some damage over time.
e.g. Bosses that use AOE or Poision or ... that you can't avoid or shield you from. Usefull in fights where you get many adds and possibly have to take some hard hits from .
2. Intellect set: You would use the intellect set in fights where you don't get much damage. With a big manapool you can keep blasting shadowbolts or searing pains. Very usefull on Boss pulls where you would run out of mana when you would use the stamina or spirit set.
3. Spirit set: Usefull when you're grinding and want to reserve on bandages or food&drinks. Also Usefull in moments between fights or after being rezzed to get you're mana and healtpoints up as quick as possible.
Then on soulshards,
Try to have at least 10-15 soulshards when you go out on raiding because people need summons,healthstones and soulstones.
Other than those, we got the Spellstone and Firestone. The Spellstone is usefull when fighting npc's that cast magic spells, or equip it for the 1% critical chance extra combined with +shadowdmg modifiers and critmodifiers on armor or weapons.
The firestone is usefull when you're all out of mana and melee is the only type of dmg you can do, also when the firestone is equip you get addition dmg points on the firespells like Searing Pain and Immolate. This only applies to Warlock that use Daggers of Swords. Staff users can't use spell- or firestones.