I'm obviously not a cheerleader... but have 2 daughters and married to a former cheer coach....

first thing i'd say is... REST. lots of rest. Not only so you can be at your best physically but so that you have the energy to overcome nerves and still project energy to the audience and/or judges.

Think teamwork. Even though you might try out as an individual you have to obviously fit into a team. all star champions are synchronized and very together. It's a bit like choir. Even if you can belt the solo you always want to blend in with the choir. Just think on that as you consider how you interact at the try outs.

Listen. Being a great listener is the most important part.

hope that helps...

from a long time observer.

Be extremely tight. MAKE FACIAL EXPRESSIONS!!
It's all star! They love it!
Be loud!
Me energetic and spirited.
And have fun :) Trust me.