2: I wouldn't say any special skills, it is just taking more shots (faster) or less (building possibly better shooting positions)
with less you often don't get a shot in time, so that you take a bad shot at the end of the clock so the overall shooting percentage won't rise much or maybe fall a bit.
Yeah, I wrote possibly. But I'd say with my experience, if you don't get a clear advantage in ratings with Run-n-Gun, Motion is the better choice. And same with Look Inside and Low Post.