Maelific Graps is the best talent.
Try to have agony (and optionally corruption) on 3 targets if possible (to create soulshards for UA spam).
When bursting, have agony + corruption on target, get 4 UA's up, use drain soul. That's the highest burst you can do.
Other than that, it's basically just a feeling of when to dot and refresh agony + corruption, i.e. at <=4 seconds is ideal to refresh, but fit it in your rotation depending on situation. For instance, if you're about to get CC'd (you see someone cast poly/fear or whatever, and the duration will run out before you get out of the cc), then refresh them before the cc lands.
Try to not hold on to soulshard cap too much. Use your UA's, optimize your damage output.
Now, this is all damage, however, you should also fit in CC's depending on the situation. I.e I use succubus, so I can seduce 1 + fear another. That's 2 targets CC'd while I'm pumping.
If you want to fit in a fear during burst, do it immediately after the 3rd or 4th UA (depending on how many shards you have), and transition into drain soul directly after.
Sometimes spamming fear on a healer to interrupt cast as they rot / take dmg from others makes them die faster since you keep interrupting their casts.
Peel for your teammates if it means they'll live.
If you're in need of soulshards, see if you can snipe the assist on a killing blow by swapping your drain soul to a dying target for a brief moment. Every target that dies during drain soul will give you one soulshard.
Against targets with interrupts (CS, kick, pummel, windshear etc.), get your agony and corruption rolling before doing anything else, as they are guaranteed value. Anything else can be interrupted. Then proceed to cast / fake, or whatever you need to do.
