I offered this advice earlier. I think it's pretty sound:
"Eat heavily, at the board if you can. Bring a six pack of beer to each game and drink liberally and noisily. Control your belches for when your opponent is looking at you. Try to start the first round after being awake at least 24 hours and don't sleep until the tournament is over.
I think that covers it.
Do that and you'll be my hero."
But there's some other advice, not as good, in this thread:
http://www.chess.com/forum/view/tournaments/first-chess-tournament-advice
I am attending an open tournament on Saturday, in which people are matched together randomly. Do you have any advice as to how I should play, and some common ettiquete to follow?