Shadowpriest DPS "Guide":
Well, I always get pmed by other spriests as to what my spell rotation is, and here is how I usually judge what to do:
If it's trash I don't bother with VE, and I use:
VT>SW:P>SWD>MB>MF>MF>MB
*note that if the trash requires healers to concentrate on the tank(s) alot then don't bother with SWD, or shield before you do it.
For Boss Fights or tougher single "trash" mobs:
VT>SWP>VE>SWD>MB>MF>MF>MB>VT>MF>MF>MB
then just repeat as needed to keep DoTs and VE up. I typically blow my racial DoT, Devouring Plague, at about 40% and typically use it with Inner Focus.
Yeah, yeah, fairly obvious, but I get messaged and asked over vent all the time how to dps as a spriest, so I figure someone on here wants to know.
Spell rotation for Hyjal/BT (credit goes to Numblocke):
In fights like archimonde / illidari council / illidan / gurtogg / reliquary, you can realistically expect to take burst of 6000-11000 dmg. For MOST shadow priests getting to a raid buffed 11k + stacking max hit and shadow dmg is a pretty big chore. lets suppose your on archimonde (since this is the most realistic) your pvp trinket is down and theres 9 seconds left on fear being cast, you pop a last sw:d / mind blast and turn tail and run, a doomfire is spreading towards you. archi hits you with grip and a nearby mage with air burst, your pot fails to remove grip, you pop tears too early and take 500 fall dmg, roughly 7500 from grip before its decursed, thats 8k, assuming you don't get feared into / through the doomfire your sw:d crits you back for 4k. gg on taking 12k dmg before someone can heal you, you wiped the raid (soul charge kills 2 people, which in turn kills 3, and it chains the whole raid).
SW: D is not a 'decent' endgame spell, and gear regardless it only constitutes approx 4-7% of a good sp's total dmg output. For the detriment on 'progression' raids, its hardly worth the hassle. VE should ALMOST always outweigh the prospect of topping meters. Also starting with a mind blast (assuming the tank has solid agro) allows for you to instant cast and IC spell before the gcd (global cooldown) triggers. this making this superior as far as dps goes. also you may want to move swd earlier since the first tick is 3 seconds after cast, and VT should be up by then. This is what my cast rotation looks like
MB>SWP>VT>VE>MB>MF>(sw:d on ssc / tk fights)>MF>MB>VT>MF>MF>MB
To help those who are unfamiliar with Spriest abbreviations:
VT: Vampiric Touch, a DoT (Damage over time) that restores a bit of mana back to the partyrelative to how much shadow damage you do, lasts for 15 seconds so you need to keep an eye on it, i.e. mana battery
VE: Vampiric Embrace, a HoT (Heal over time :P) that restores some health to the entire party based on how much shadow damage you do, makes you a health battery
SW:P: Shadow Word: Pain, a DoT, that lasts for 18 seconds (longer if talented, which it will be) and is your main DoT, keep this up with VT to max dps
SWD: Shadow Word: Death, an instant shadow damage spell (Spriest fireblast) but it will deal the same damage back at you if the spell doesn't kill the target, i.e. do not use this on Curator as I know from experience you will die from a 9-11k SWD
MB: Mind Blast, Spriest shadowbolt except we can't spam it due to the 8 second (i have it 4/5 imp MB so my cooldown is 6, this is recommended) cooldown.
MF: Mind Flay is our filler spell, if MB is down and all DoTs are up, spam this until you need to recast a DoT or MB
DP (Undead only): Devouring Plague, Undead priest only ability, a DoT that is considered a disease, it deals damage AND returns health, on a 3 min CD and costs 1.1k mana (due to the high mana cost I use DP with Inner Focus so it costs nothing), also is instant cast
Starshards (Night Elf only): Starshards doesn't have an abbreviation, maybe some have one for it but I don't, this is a Night Elf priest only, instant cast, no mana, DoT on a 30 second CD, cast this alongside SWP and VT