Bring at least 4 mags and around 125 rds of ammo for each class/division you shoot. The extra ammo is in case of a re-shoot. Like Alex29 said read the rules online or in the annual. The RO's will be helpful where ever you shoot. Tell them you are new when you go to shoot. They will talk you thru it. Don't be afraid to ask anyone standing around at the stages for advise or help/info. Watching is a great help. Always have your mags loaded before you get up to shoot. GSSF is a friendly group of people. Don't worry about a miss or going slow. My goal is to shoot better than any of my previous personnal bests. I don't worry what others shoot, I shoot against my own times. I can only hope to improve, and have with practice and shooting matches. My adice would be don't try to beat a Grady, Butch or Alex29 your first time out. Shoot your best and the rest will come as you progress. Heck randoms make it worthwhile. I win money in randoms every year I shoot and haven't paid a yearly membership since my first yearly 8 years ago. Reason being is I usually win a random 2 year extension. Look into the GSSF indoor matches also.
how's that hope and change working for you?