Hopefully this will be the first of many races in your future. The important points have already been mentioned.
Give yourself plenty of time before the race so you're not in a rush to get to the start line. Wear clothing & shoes that you've already tested out on training runs, you don't want any surprises on race day.
One thing I notice novice runners doing is stopping in the middle of the race course to take water, this can make for some quick footwork if you're behind them.
If you need water, run to the side of the course by the water tables so those not stopping can get by.
Enjoy the experience & the people, with each race you'll learn something new that you can keep in mind for your next race.
Best of luck to you!