Some things that have always been good for me:
Always show respect to ALL those around you, whether they outrank you or not. You represent yourself and and your school when you compete, so make a good impression.
You are also an example to younger students coming up, so be aware that others may be looking to you to know how to behave.
If you can read the rules beforehand, do so. If they are told to you, listen carefully. If given a chance to ask questions and you have one, ask it.
Be a good sport, win, lose, or draw. Sometimes you will think you've performed The World's Greatest Kata, or landed the World's Greatest Kick and the judging will be against you. It happens. Don't let it bug you.
Observe and learn all you can from the performances of others. Maybe a move or strategy you see someone else do will work for you, too.
Hope this is helpful.