I think that in preparing for a tournament, the following points are important:
1. Don't waste time preparing openings. Get out of book straight away by playing b3 followed by g4, or b6 and g5 as black. Your opponent won't know what's happening!
2. As you'll've done so well with the above opening, no need to work on endgames either.
3. For most players, a tournament is a chance to meet fellow chessers, have a few drinks and basically enjoy themselves. However you don't want to look like a Larry Lightweight on your first night down the pub, so it's important to get plenty of drinking practice in the run-up to the big event.
4. On the big day, it’s important to be motivated. Listening to some motivational music like that training montage from Rocky 3 or 4, you know the one where he chops firewood, should get you fired up.
If you can have this running through your head all day, you’ll be unbeatable.