Well I'll leave this
here for starters. It's end-game driven, but much of it will still be relevant as you have many of the end-game spells already. Most of this information came directly from there. Some things it lists:
Shadow Bolt (cast once at the beginning of a fight for the buff - you'll want 3 points in Shadow and Flame, a Destruction talent) -> Haunt -> Bane of Doom -> Corruption -> Unstable Affliction -> Shadow Bolt/Drain Life Filler
[Glyph of Corruption]
[Glyph of Unstable Affliction]
[Glyph of Haunt]
[Glyph of Life Tap]
[Glyph of Shadow Bolt] - Unless using Drain Life filler
[Glyph of Soul Swap]
Much of the rest of any advice I'd give is 'knowing your class' related.
For example are you using AoE and single-target spells at the appropriate time? Are you continuing to DPS when you have to move during a fight? Are you deviating from the above rotation when the target isn't going to live very long? (No use dotting up a target that dies fast). Do you have good up-time on your DoTs during longer fights? (You don't want them falling off but you don't want to refresh them too early either). Which pet are you using?
I should also add the disclaimer that I've primarily played Destruction. Edited, May 9th 2011 10:14pm by someproteinguy