alot of advice will be given by many of us, like cardiovascular training, etc. but I'll give you a bit of advice (take it or leave it) that is a bit less common. While cardio is well and good, don't neglect weight training either. Strength is important, but technique will be critical.
Ready for the uncommon advice? don't drop weight classes, unless you TRULY have the fat to spare. And even then do it slowly. By the time kids spit, run, starve, and sweat themselves to the next wight class down they aren't any stronger, and often time weaker than they would have been just staying where they were, and can also lose a serious mental edge.
Also don't try to learn every single move out there, especially your first year. go for three basic takedowns, three basic pins, and three basic escapes/reversals. etc. don't overwhelm yourself.
Another pointer- talk is cheap. ignore at least 90% of it. screw what they say the other guy's gonna do to you, think about what you're gonna do to HIM. Everyone is quick to say not to underestimate your opponent, well ya' know what? don't overestimate 'im either.
And finally....don't go out there and get pissed off. it actually weakens you in the long run. the mat is no place for emotions, if someone talked garbage, or whatever, wait 'till after you beat him to get angry.
Listen to your coaches, and never quit trying to find ways to improve yourself. If you find yourself in doubt of what a coach has to say, ASK YOUR PARENTS. I had a few incidences in wrestling I wished I'd deferred to my parents judgement.
and finally....be careful of your knees. that means don't twist or overtorque them. God only gives ya' one set, and once you break 'em, they aint never the same. (learned that the hard way...just before States, my senior year)
Anyhoo, best of luck to ya'!
BTW, what weight class are you looking at?