Eat, drink water, and listen to a cheesy pump up song (All Star and Eye Of The Tiger are personal favorites)! I also like to watch a lot of other riders in the ring I am in just to see what is happening and how things are set.
I personally think of how hard I have worked at home and keep repeating to myself "I can do it, I will do it". I also think of what I have to do so this keeps me busy and doesn't make me feel pressure and anxiety.
A big tip is to eat the day of. It may sound weird now but the day of you feel nervous and when you don’t want to eat, you will feel worse. So that is my main tip but also practice makes perfect. Sometimes shows don’t always go your way but that is part of the game.