Well,first of all,in raid or instance you wont be the one taking damage,tank will be,so if you're raiding you wont be needing talent like demonic embrace or iHoT (improved Howl Of Terror) or if you're pvping you wont be needing talent like Malediction...
Basicly,for pvp you need talents that directly help YOU to live longer,take more dmg etc and for pve you'll be focusing on getting as much damage as you can.Example is
SL/SL build.Its great for pvp ,but for pve its no good.
Then you have 0/21/40 build that most good (very good) locks use in raids and is cmpletely useless for pvp.
Then you have build like
this wich is my fav build as you can use it in pvp and in pve.
You'll get hang of it during time.