Etiquette
When playing someone who is 1.0 or more lower than your rating, go easy on them and match their ability. Work on a specific area of your game that needs improvement. For a major challenge, make the Transition Zone out for you except on the serve and go from there. You could also stay in the Transition Zone and reset all shots into the NVZ.
If you have to cross another court to get to the exit or to your court, wait until the point is over and hurry up since you're delaying their game. Call out, "Crossing!" so people know you are behind them.
Try to find a game with players that are at or around your level. If they are much higher or lower than your level it won't be much fun for you or the other players.
Do your best to remember the score, whose serve it is, and if they are a 1 or a 2.
Regarding line calls, if it's close, just call it in. If you and your partner didn't see it, call it in. If you and your partner disagree, the ball is in.
Don't celebrate or laugh at your opponent's unforced errors. This is common and is really rude.
When playing doubles, ALWAYS keep any comments you make positive. Never berate your partner for making mistakes. Avoid saying "good try" since that can be patronizing. Your partner knows they messed up.