There are quite a few things to do to improve your results as well as enjoy the tournament.
On the physical side stay well rested and well hydrated during your game. Eat plenty but keep it healthy. When it's not your move walk around and look at other boards, resting your tired eyes and getting the blood circulating. Do a light exercise in the morning before your games even start. Lastly if you didn't sleep well maybe have some caffeine ready to go.
As for mentality, don't worry about anything except having interesting, exciting games you can show your chess friends when you get back from the tournament. Win or loss, make sure you play what you think are the best moves, even if they get very complex. Don't look at your opponents rating just briefly glance enough to see your board color and the table you're playing at. Knowing their rating and letting it distract you won't let you make better chess moves over the board. Keep your entire focus on the game you are playing. Once you finish a game, win or loss, don't think about it too much and relax. You just played a physically exhausting game, recupe the best you can and focus on getting your energy back. As long as you tried your best that's all that matters. Results are just check marks for one side or another, what really matters is being brave and showing determination to play the best move you can see, and improving your understanding using those games once the tournament ends.
At least I try to do all these things when I play tournament chess, I've even come first in my section a number of times.