I second almost everything above - especially Raiden.Kaminari's stuff. But what especially get's to me is Stray Balls. Unless you've got barriers between courts, most tournaments have every court in session, and balls flying everywhere. It's sometimes impossible to play a LONG point without a stray ball rolling through your court.
So, keep an eye on YOUR balls.
If your ball is rolling towards another court, stop it before it gets there.
Don't hit sharply angled cross-court shots if you're playing in the middle of a long string of courts.
If you see someone in danger of stepping on a ball they don't see, warn them.
Return balls promptly that are hit onto your court.
Apologize for your balls that wonder onto other courts.