Shadowpriest.com is a wonderful resource.
Your #1 priority is to keep VT and SWP ticking. After that, use Blast and Death when they're up, and fill in the rest with Flays. I also generally keep VE up at all times. If you're having aggro problems, drop Death and/or Blast out; same with mana problems. Get a good DoT timer (I recommend ClassTimer) and get used to watching it religiously while still paying attention to the fight.
Get Quartz Casting Bar and set up macros like this:
#showtooltip
/stopcasting
/cast spellname
That's an incredible way to boost your DPS once you get used to it; it basically forces the spell off on server time rather than client time (the spell is done server-side but not client-side, and forces it to end early but still go off client side, counteracting most latency above about ~50ms).
Get lots of mana pots, and get used to getting and using them. Use them when they'll first give you the max amount (as soon as you're down 3000 mana). I spend about 120g of mana pots a week, plus about 200g in flasks and another 100g or so in other consumables.
We can and do outdamage other classes up until SSC/TK at least, though as others get geared and spec into pure raiding builds we start to fall. I'm usually top 3 on damage in Gruul, behind a lock or two, but then again some of our mages are a bit stubborn about keeping their PvP specs. In Kara it really depends on the fight; I have yet to actually live through Big Bad Wolf and Attumen, and fights like Shade and Illhoof and Maiden favor certain classes, Prince is hard on spriests, though we're great on Curator and especially Netherspite (2900dps wtf?!).
Oh, one other thing. Try and keep Blast and Death on cooldown, but be very aware of fight mechanics with Death. Use it very carefully on Curator (evocation, especially if you were just Hateful Bolted), Prince (enfeeble and axes), Netherspite (blue beam + SWD crit = 34000dmg on yourself :D), Shade (Arcane Missiles), Magtheridon (cube clicks/banishes), and so on.
Edited, Oct 19th 2007 11:56am by lsfreak