I just looked at the first boss
1. you find the correct opener here:
http://www.ravenholdt.net/assassination-guide/
2. with shoulders you just want to press Envenom as much as possible
3. you have to prepare a bit for Kingsbane, if your dots are about to fall off refresh them before Kingsbane
4. During Kingsbane you want to keep up the Envenom buff up (you should have a timer for the buff)
Besides the wrong opener/vanish usage you're spamming buttons to much.
Rogues are not DHs or Warriors, you don't have to press a button every second, if you have the Envenom buff, your dots are up, you have like 40-80 energy and 4 cps.... just wait 2-3 sec before you Envenom. This way you will have a better uptime on your Envenom buff.
Again
energy is potential damage, if you don't overcap you won't lose damage. Try to plan 2-3 finishers ahead.