Of the original list, watching the ball all the way to contact is number one for me. Really focusing on that contact spot and ripping my racquet to that spot - when I do that things go well more often than not.
The feet are the next important thing. Getting set-up in the proper position quickly, not "walking" to my shots is key.
One overarching thing I like to consider is that I work on things I can directly and completely control. I can watch the ball. I may not hit it well but I can force myself to watch it. Likewise with moving my feet, how I set-up, or the swing path the racquet makes. It's true that I may do all of those things right and still miss the shot, but I've done the things that I can do to give myself the best chance of hitting the ball well.
OTOH, I can't directly make the ball go over the net. My mental telepathy sucks. I really can't even make the ball hit the center of the racquet. Those are really outcomes of doing other things correctly. So if I miss, or shank, I try not to worry about it in and of itself. But if I don't watch the ball, or don't move, or don't set-up well, etc., then I try to fix that the next shot.