I haven't been at the Umpire pos. for several yrs. but I usually picked 2 or 3 linemen to watch. Then I would focus on the other 2 or 3 the next play. Yes, you cannot see everybody on every play but don't get tunnel vision keep you eyes moving and don't focus on one player.

As far as being nervous, I have been doing this for 20 yrs and I still get the first game jitters. Especially this year, since I have moved to a new part of the state. I have to prove myself all over again. Don't worry it will get better as the season goes on.