Showing Horse for 1st Time, Advice?

My advice would for western pleasure and halter would be to make sure you look clean cut. No dirt on any tack, you, or the horse. For all riding classes, make sure you have the helmet (if they require one) and ride your horse around the grounds by the arena to make sure nothing really spooks him. At my fair during gaming classes we have to run with dirt-bikes firing up behind us..so hopefully you don't have that. Showing can be a ton of fun, just relax! :)