[U]Single Target:[/U]
Keep SnD up, keep Rupture up and use Envenom when you have spare CPs. Don't clip Envenoms. Use Mutilate to build CPs, or Dispatch if you have a Blindside proc or the target is below 35%
The priority system is as follows:
1-2 CP SnD if not already up > Maintain 5 CP Rup > Envenom
There are a few things to note here. It's better to have any kind of Rupture up than no Rupture. If you can, only use 5 CP Rups, but if you lapse in keeping it up and you have no energy, no Rup and 3 CPs or less, go ahead and Rup. You run the risk of not getting energy returns from Relentless Strikes, but it's better than languishing for 3-10 seconds because you have no Venomous Wounds procs. If you have 3+ CPs and will soon have the energy for another Mutilate or Dispatch, you may want to wait though. It's one of those instinctual moments. The best solution, however, is to just watch Rupture carefully and make sure it doesn't fall off.
Slice and Dice requires no maintenance most of the time as Assassination. Any Envenom, from 1 CP to 5 CPs, will refresh SnD to a duration of 36 seconds, the max it can be with set bonuses or other effects. So it's usually a good idea to only get a low CP SnD rolling and then quickly maximize it with an Envenom.
[B]Building combo points is simple:
Dispatch (Target below 35%, Blindside proc) > Mutilate[/B]
[B]For opening out of Stealth[/B], you should be opening with Mutilate. Why Mutilate? Mutilate has double the chance to apply poisons, costs less energy than Ambush and can proc Dispatch, so Ambush is the weaker option in this case.
Listen up!
[U]Multiple Targets:[/U]
Continue with your single target rotation, replacing your CP generator with Fan of Knives. Maintain Rupture on 1-3 targets. Alternate between Envenom and Crimson Tempest for your finishers when not applying Rupture.
When you're engaging more than one target, your rotation stays more or less the same. You're going to be maintaining Rupture on 2-3 targets. This will give you more than enough energy to spam Fan of Knives constantly (Which grants 2 CPs now when you crit!) and extra damage through Venomous Wounds. More Fan of Knives casts means many more poison applications, which is your #1 source of damage. Only use Envenom if you're at risk of losing SnD or if none of your Ruptures need to be refreshed. Use Crimson Tempest if you get 5 CPs and the Envenom buff is still up.