Muti PVE
Keep SND Up
Keep Rupture up
Use Instant and Deadly Poisons
Use Envenom on 4 or 5 combo points
Use Backstab when boss below 35%.
Build
Combat PVE
Keep SND Up
Keep Rupture up
Use Instant and Deadly Poisons
Use Revealing Strike on 4 combo points
Use Eviscerate on 5 combo points
Build
Muti PVP
It is almost impossible to keep both SND and Rupture up while Stunning and Kicking your opponent at the same time and also using various other abilities.
You don't envenom as much because you are using the combo points for kidney, so deadly usually gets full 5 stacks before you need to envenom again. That's why Master Poisoner is situational.
Most likely you will 2vs2 or 3vs3 in a team with a caster. So take Master Poisoner mainly for the extra spell damage. If you are in a 2vs2 with a priest that doesn't go offensive but goes mana burn you can choose between Improved Exposed and Murderous Intent.
Use Eviscerate mostly in bg's and don't go SND, SND + Envenom is more for arenas in which the oposing team has a healer.
Build
So far, muti seems superior.