When's the tournament? If you have plenty of time, start upping the intensity when you train.
Understand that competition is going to be an entirely different beast from when you roll on the mat. I didn't really do any sports (other than Kindergarten-2nd grade) until I started martial arts, so I still struggle with the competition mentality (though I'm getting much better).
Since there's a time limit (I'm assuming), and since the other guy really wants to win, it's going to be INTENSE. When you get onto the mat, be ready to go all out. Be intense, but be smart. You should still be using your techniques, but just be ready to do it with maximum effort, and maximum speed. You're going to be way more tired than you get in the gym.
Eat foods with a low glycemic index, 1 to 2 hours before your first match. If you don't feel like looking up these foods, get something like a Power Bar, Cliff Bar, or Balance Bar (I swear by Balance Bars, they give me so much energy). You need carbs, but carbs that will burn slow. Avoid that energy soda shit. Gatorade and water are fine (but sometimes the competitions are in a basketball-type gym, and you can only have water.) Trail mix is also really good. Remember, 1-2 hours before. That's how long it takes to be digested.
When you're getting yourself pumped up, don't do it too early. Believe it or not, your emotions can actually burn more or less energy, depending on what they are. I usually like to listen to Hatebreed, Throwdown, Killswitch Engage, or other really hard bands. But I used to get myself pumped up from when I got in the car until I stepped on the mat. This really burns your energy. You can't just keep yourself in a rage all day. Stay relaxed until maybe 10 or 15 minutes before your match. Then put in the metal and get yourself pissed.
WARM UP. I can't stress this enough. You should walk onto the mat with sweat dripping from your forehead. To step onto the mat with cold muscles, and then exert yourself to the extreme degree you will in competition will burn TONS of energy, and you'll gas like crazy. You'll feel like crap and won't be able to perform your best. Jump rope, do some grappling drills, jog, whatever. Wear lots of layers so that you get your body heat up fast.
Make a game plan and VISUALIZE. Your plan should not be "I'm going to go out there and see what he does." No. Why should you play his game? You put in your time, your sweat, and your blood, like anyone else, and this is yours. When you're much better than someone, then you can play their game, in the gym, because they can't beat you anyways. But in competition, when you're evenly matched, you need to physically impose your will. Create a solid game plan based on your strengths and weaknesses. For example, my low single leg takedown has caught me in a guillotine twice in competition, because I didn't do it right. So, I avoid even doing those. Create a backup plan for everything that could go wrong. The more intricate and thought-out your plan is, the better chance you have of winning.
Once you come up with this plan, you need to VISUALIZE (for the second time). Run the match over and over and over in your head. Imagine it as vividly as possible. The more times you run through it, and the greater the detail, the more prepared you'll be to call upon your muscles to do it.
Don't doubt yourself. It's easy to do this. You're worried, you don't want to look bad in front of people, we all know how it feels. Have confidence in yourself. Remember that the other guy is nervous, too. He's human, and he's not infallible. You can submit him.
When you step onto the mat, whether you look into his eyes or not is up to you. Wanderlei Silva, as we all know, likes to try to intimidate his opponent. Other guys, like Kazushi Sakuraba, prefer not to look into their opponent's eyes, not because they're scared, but because it's widely believed that it works your nerves up and throws off your focus. It's up to you. When the match starts, remember your game plan. Stick with it. Use all the effort that you have. If something in your plan falls through, don't sweat it, just fall back to the next step in your plan.
Even though you should be going all out, personally, I've found that in grappling, you're better off waiting and anticipating your next move. In wrestling, we go all out, nonstop, but I've found that in grappling, if I just try to muscle through a move without stopping, the other guy knows it's coming, and defends it. If you instead anticipate every part of the move, make an opening or distract him, and then EXPLODE with the move, you have a much better chance of catching him. For example, I wouldn't grab his wrist and just start muscling it back into his chest looking for a triangle choke. He knows it's coming, so he's going to defend. Instead, I'd fake something else, or anticipate the move, and then SHOVE his arm back as fast as I could.
Relax a little bit, and observe your breathing pattern. I've rolled with guys who get so worked up they forget to breathe, or they sound like a suffocating bull. If you breathe, and control your breath pattern, you're going to expend much less energy.
And remember, have fun. I have a blast grappling. I like it so much more than wrestling. Whether you win or lose, just have confidence that you're going to do the best you possibly can, and that you're going to make it a great match. Some of the best matches I've ever been in, I didn't even win. But the match itself was great, and so I was happy. If you lose, don't doubt yourself or your ability, instead, see where you went wrong, shake your opponent's hand, and come off the mat with a smile.
If there's anything I missed, there are plenty of great tips on competition on
www.grapplearts.com
Good luck!