Most of the major stuff has been covered already- muzzle discipline, trigger discipline, thats 90% of it.
My personal peeve aside from the above is people picking up your brass. Ive lost count of how many times Ive had to stop shooting to let someone know I save my brass and just because its hit the ground doesnt mean it somehow belongs to them now.
My personal noobs mistakes- Changing out or checking my targets excessively. Didnt realize how much of a pain in the ass I was being until coming across a couple of people doing the same thing. Also didnt know that during a cease fire you needed to be away from the line. I knew the rifle had to be unloaded with the action open, hands off, etc but I just kind of hung out at the bench until I was politely corrected by someone.