I'll add a #8 alongside the very worthy (7) points he makes.
#8 - Visualize.
In preparation for a match visualize the match and decisions you may have to make. Picture entering the field. Air is warm, sun is out, and you can smell the fresh cut grass. Visualize inspecting the teams before the match and having a nice pre-match conversation with a coach or player. Feel the thrill of that first whistle to start the match. Imagine that hand ball that a player tries to get away with on your blind side. Picture in your mind that goal by the #10 and before pointing upfield, looking to your assistant to verify it was a good goal. Go through cautioning a player for that hard challenge that has no place on this day. Finish by visualizing the final whistles and shaking hands with your teammates ... all of them ... players and referees alike who worked for 90 minutes together for a good match.
Imagine the good and the bad and how you are going to deal with it that day. Play it in your head before you walk into the field. If you find yourself waining during a match, replay that part to bolster your focus and confidence.
Then do it.