Without reading the other advice...
Find out where the ground is day before, so you can plan the journey properly, aiming to get there say an hour & 1/2 before you're due to shoot. Check the weather report.
As you're shooting PM, sign in and get that sorted, then you can find your lane number. You'll be able to then walk the course, find where that start lane is, and the plinking range.
Get the gun filled up, check she's ranging and shooting on the level and you're happy. Get some food & water in you for the afternoon.
You're bound to be nervous. But almost everyone is first time. Just relax as much as possible and keep eyes and ears out for tips.
Anything you want to know, just ask... either a marshal or you can find me on the line swearing at a springer.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep