As some others have said, start in an early group- make sure you point out its your first race to the organiser, and dont try and big yourself up! Take advantage of the few laps you'll have to get used to riding with others, if you manage to hang on when it all comes togeather, concentrate on staying close with no sudden movements or braking. you'll probbably get 'advice' from the other riders if you do something wrong!
Good luck, and enjoy it! If you get dropped this week dont give up, it may take you a few races to get used to it and learn how to ride etc.
The first time you dont get dropped and finish in the main group is a real buzz.