Currently a 14/14 Holy Paladin and 10/14 Discipline Priest in Siege of Orgrimmar
Formerly voidspark - 8/8 Demonology Warlock and Restoration Druid in Dragon Soul
I don't agree with some things written in this thread. Starting an encounter with dark soul and SB:SS is a DPS loss as you should wait for your weapon / trinket / cloak proc before using dark soul. Also the more agony stacks you already have the more dmg you get out of dark soul.
My rotation: CoE -> agony -> cor -> UA -> MG (at that point I have my cloak and weapon proc maybe even mithril watch) -> dark soul + lifeblood + on use trinket -> SB:SS -> haunt -> MG -> MG... before the procs run out I refresh dots with SB:SS again. I don't refresh manually as some of the shorter procs would run out.
Before dark soul is ready again I always drain soul to regain shards. I'm trying to have 100% haunt uptime while dark soul is active. Having timers for the internal cooldowns for cloak / weapon procs also helps to time dark soul for max effect.
Refreshing dots at the right time to get the most out of your procs is in my opinion the best way to boost damage.