The most important advice I can give you is: Keep cool, very, very cool!
It is surprisingly easy not to. The whole atmosphere is quite different from a normal money game. In that game you probably know your Opponent well. But in the tournament you may well be drawn against somebody whom you don't know at all. He may be much better than you or much worse, or at any rate you may think so. If you think he is much better than you are you may get flustered and play quicker than usual, because you are embarrassed to keep him waiting over what may be, to him, an absolutely obvious move. It's likely that quite a few people are watching, and you may even be tempted to make rather grand moves to impress the onlookers. If, on the other hand, you think that your Opponent is a great deal worse than you and he gets ahead, his outrageous luck will certainly drive you mad, so that you may play stupidly for that reason. It happens over and over again.
If you are taking the tournament seriously, arrive there very fresh and do not drink unless you've proved conclusively that it works. Have no appointments. Be in no hurry. I am not telling you how to enjoy a tournament. I am telling you how to win it! There are tournaments which are worth 1000€ or more to the winner, and if you play in one of those surely it's worth while to cut out a whisky and soda, and even to postpone a date. Both will taste better after a win!