Be sure you breathe while you're skating, and SMILE! This is supposed to be fun. Also try to remember to bend your knees; this and the breathing help you avoid shaky leg syndrome. Also, it helps to have a plan for your warmup - find out how many minutes you get, and then work out a plan with your coach on how to spend that time. My first competition, I didn't know that and I just wandered around the ice in a terrified, shocked mess making the same failed attempt at one element over and over until my coach called me over and told me - do this, do that.
I hope you have a wonderful time! Enjoy the entire experience. I always get off the ice after I compete and wish I could get back out and skate my program again.