I suggest you get a helmet and try not to get barrelled over. Seriously though, first lesson I learned was stand on top of the ball until the ready for play and then move back, keeping an eye on the ball the whole time. We actually had a DT move the ball back so the offense had 4th and 1 instead of 4th and inches. Needless to say, he had an early exit. Follow your keys, study film, the guards will tell you whats going on every time, this was kind of easy after being a linebacker in my playing days. Call the holds that affect the play, if your following your keys these are the only ones you'll see. The umpire does a lot between plays, which takes some getting used to:
1. Help referee with 7 on the line
2. Eligible numbers
3. Chin straps, mouthguards
4. Who is in the free blocking zone(different this year)
5. Other things I'm sure, not off the top of my head
P.S. If you want a good tool to help with keys and mechanics go to
http://www.nfhs.org football and check out the 3 powerpoint presentations on mechanics and keys
Good Luck
[Edited by abergman on Aug 22nd, 2001 at 01:43 PM]