Priest
Overview
Specs, Stats, & Rotations: Discipline(Healing)
Specs, Stats, & Rotations: Holy(Healing)
Specs, Stats, & Rotations: Shadow(DPS)
Stat Priority Int> Spirit(to 17% hit)> Hit(to 17% hit)> Haste> Mastery>Crit
After you cap your hit, load on the haste, your dots will tick more over their duration as you acquire more haste (the big breakpoints are 21.4% haste which give you 2 extra ticks on all dots and 38.7% which give you 3 extra ticks on all dots).
Your spec should look something like this (8/0/31) with 2 extra points to put where you want.
Prime Glyphs are Mind Flay, Shadow Word Death, and Shadow Word Pain.
You will want a dot timer of some sort (I use Inline Aura). When targeting low health mobs you want to cast mind spike 3 times and then cast a mind blast with a 90 recent crit chance. Most of the time after that the mob will be in SW:D territory.
For longer fights open with Shadow Word:Pain, followed by Vampiric Touch, then Devouring Plague, Mind Blast, then Mind Flay and then just refresh all your dots and use Mind Blast on cooldown. You can clip mind flay to refresh dots (always refresh with less than 3 seconds less but never let them fall off) or cast Mind Blast but try to clip right after a tick.
A word on running out of mana, I have been talking to several Spriests over the last couple of weeks and they are having problems with mana conservation. If you are generally having mana problems work Shadow Word Death into your rotation after the Mind Blast initially and then when it's off cooldown, don't clip your Mind Flay ticks for SW:D, it's not really a DPS gain, but a mana replenishment.
Dispersion can be used pretty much whenever you want, try to save it for unavoidable Boss damage rather than mana replenishment (or get tricky and learn the fight and use it for both). And pop your shadowfiend whenever it's off cooldown :D
~ Any other questions (and I mean seriously I love my shadow priest) you can message me here, Twitter, or just look for Lasciele or "shard" in game.
Tips & Tricks
Macros
Some handy-dandy macros:
Spammable Mass Dispel: Keeps targeting reticule from disappearing when spamming the button.
/stopcasting
/cast !Mass Dispel