Along the way, things which have helped me (they all seem so obvious now!)...
If you're on the bottom in a bad position, control their hips. Hips = balance.
Be prepared to let things go, don't get caught up in attacking one thing. I.e. you've got their back but they're escaping... go to mount, don't try to hang on to the back and end up being reversed. You're attacking an armbar but they're pulling out... switch to triangle or omoplata, or sweep them.
Grips are all important. The only time you should let go of a grip is to move to a more dominant or more useful one.
Always attack. Always. Don't let your opponent take the initiative at any point in the fight. If they are in a dominant position this means you should be constantly moving to escape, make them fight for a good control don't give it to them. If you're in a dominant position, constantly threaten subs so that your opponent has to defend that before starting an escape.