My first game this week

[wisref2]

Good stuff from mcrowder. A few of my own:

Watch the game, don't watch for fouls.
Keep your eyes moving - prevents tunnel vision.
See it before you call it.
It's your first game, so the most important thing is to have fun (as it is in your next game, and every game after that).
Ask questions of your crew at halftime and after the game.
See the ball EVERY TIME before you blow the whistle.
See it before you call it.
As umpire, you probably don't have to blow the whistle - so don't. The wings will take care of the whistle.
See it before you call it.
And of the best lessons I ever learned was in a clinic this summer (as I'm going into my 24th season!) - don't complicate the game. You'll understand this better after a few seasons. But it means don't make complicated calls when a simple one will do. ie - receiver catches the ball just as he gets hit, the ball comes out - don't complicate it by ruling catch and fumble, just rule it incomplete.
And finally, see it before you call it. No guessing.