I thought I'd throw my .02 in here briefly from my racing days...
Great points about the bike guys, but I thought I'd add a couple more subtle points...
General Bike Maintenance - Very key. Don't just ride it during the week and chuck it in the garage until race day. Prep it throughly before race day and you'll feel alot more confident when you go to the line... Filter clean?? clean it; oil changed?? change it(if necessary); haven't repacked your silencer in a while?? pack it; make sure every bolt is snugged down; clutch and throttle adjusted; brakes!!; etc. I know it helped my confidence that the bike was ready to go... esp. when you see some guy w/ a zip tie holding on his side panel or w/ a beat looking bike... you are already ahead of that guy in the mental game.
Your health and fitness - A nice after market pipe and a fresh top end will give you nice crisp power and an extra couple ponies, but if you wear out before the checkers, it won't really matter. Even as a teen, when I started eating right and training, I saw a difference in my results. I didn't go crazy, but adding a couple days of running and weights to my weekly routine and eliminating some of the junk food from my diet actually did help. I HIGHLY recomend eating a healthy meal the night before and the morning of race day as well as staying well hydrated throughout that time (= lots of water, not gatorade, sodas, energy drinks, etc.). You might not notice it in the throttle of your bike, or even feel much different yourself, but you will notice it at the end of the moto.
Oh yeah, practice lots... especially starts!!!
Good luck, be safe and have fun!!!