a wise man once said "I am the wisest of men for all that I know is that I know nothing at all...
once one reaches the level of master(instructor/teacher), one should not hesitate to ask questions of one's peers and continue to learn all one can about one's chosen field of mastery."
Never was truer word spoken!
This may be redundant, but take a friend. Sometimes it's very hard to correct faults when you can't see what's happening yourself. You might be the range master or controller, but someone has to stand and watch how your students are gripping the firearm, what their finger is doing on the trigger, etc. That can be hard to see from behind a line of shooters.
I'd also add a tape measure. If you're shooting on an outdoor range, knowing distances from the line to target can be helpful. Maybe even small traffic cones to mark the lines where shooters should stand.