[Best Single tip for running a good stage]

Make a stage plan and shoot it, stop pasting when you're called in the hole (squad size permitting) run through your plan. Whatever you do, do not change your stage plan last minute.

[Shooting Groups in practice.....ideas?]

Use the time to practice calling your shots. Take a shot and past where you think you hit on another target then compare to where you actually hit on the target down range. I know it sounds silly but everyone does that dance on the last shot before exiting a position because they don't have the confidence in where the round scored (or they wait to hear the round impact steel.

[Do you focus on the dot or the target?]

I didn't see it mentioned so I will recommend a drill that was shown to me by a friend. Cover the glass with something (paster, tape, whatever) and dry fire. This will force you to look at the target.