focus on your breathing. even if you think you're calm and ready, I bet a dollar when you step up to the line your heart is gonna be going a mile a minute, and this is guaranteed to sap your energy. my advice is to not think about ANYTHING except using slow deep breaths to slow your heart rate down. in addition to helping you not gas out in the first 10 seconds, it has a calming effect, which ought to improve your performance.
also, and this might be wasted breath because if you manage to follow this advice your first tournament it will be amazing, but keep your arms relaxed. everyone goes in thinking "Ok there's no way I'm gonna allow this guy to get close enough to throw me." and even though you're probably not consciously thinking that, I bet it'll be going in the back of your mind, and you'll go out there and stiff arm like crazy, and as a result it will be very difficult to get in any attacks of your own. so instead of thinking "I'm not gonna let this guy anywhere near me" think "I'm gonna get out of this guys way, and not be where he expects me to be."
and just remember it's your first event, so nobody is expecting anything out of you. if you lose big nobody will be disappointed. if you play ultra defensive and don't get thrown, but don't throw anyone either, nobody will be all that impressed. but if you go out there and attack boldly and frequently, even if as a result you get countered and lose big, people will be impressed. go out there and go for broke, you have nothing to lose by doing so.
and also, when you find out you're 4th or 5th in line, go to the bathroom and try to empty your bladder. trust me, the words "I gotta pee" are the last thing you want running through your mind when you're in the middle of a match.
lastly, try to have fun. if you're not having fun, what's the point? it's not the world championships, it's a novice tournament, relax, try to meet people in your division (and be friendly with them) and have as much fun as possible.