First, congrats on your upcoming first show (unless it has already passed, and if so, how'd you do?).
One tip is to make sure you put the work in before the show to make your show a success. Get your heifer where when she stops she you don't even have to stick her legs because she is ready or you may only move one leg.
Don't take your eyes of the judge.
Know your animal inside and out. If she is bred, know what she is bred to and when. Know how much you feed her, what you feed her. Her Date of Birth, or as close as you can get. Know the parts of the cow as best you can. I won showmanship once because I was the only one in the class who knew where the stifle muscle was (I hope that's not the only reason but it helped).
Be confident when you are in the ring.
Get to the show early in the morning so you have plenty of time to get your heifer ready. Sometimes show day prep doesn't go 100% perfect (full wash rack, power goes out, whatever), but if you are there early enough to have time to wait out issues or adjust to them it will make you more relaxed during the day.
Showing is a great way to learn a lot. Not just about cattle or showing, but life lessons as well. Enjoy every minute of it! GOOD LUCK!!!