Nervousness is a good thing. It means he cares.
Develop a game plan for when the nerves come.
- Go over the plays/formations
- Think about coverages or reads he'll make in the game
- listen to peaceful music (this really helped me. I never needed help getting amped up for a game)
Nerves come because his mind is dwelling on the unknown and trying to figure it out. If he gets nervous 2-3 hours before the game, work out a routine that takes that long. Having something to do/prepare will kill the nerves just like taking the first snap.