It looks like you will be starting fresh from ground zero.
So lets look at racial abilities that help priest-
DWARF- Fear ward. I think this is best for PvP. When it is up you cannot be feared.
Night Elf- Star Shards, whoopie... Shadow Meld, not bad for PvP but not as strong as fear ward.
Human- Desprate Prayer, insta self heal, not bad for PvP, not as good as fear ward a slight edge over Shadow Meld.
I would start with a dwarf if I had it to do over again.
To level get you get a mace and try to get a wand as quick as you can. The first 20 levels of being a priest are the hardest and the first ten might be the most frustrating because you do so little damage.
Get to 10 and then we can talk about talent points!!!
First 5 go into Spirit tap no questions asked.
Next 2 to improved Shadow Word Pain again no question for these...
The next three are purely personal choice between Blackout (the one I would choose) and shadow focus.
The next 8 go into the level three spells however you personally want to do it either one each or max one out. Personally I would go Mind Flay first, then alternate Improved Mind Blast and Psychic Scream.
I will do more later, if there is a need.