RJM's list is solid.
a couple of surprises, though. One: our most independent kid (we thought) became the most needy while he was away. We learned about this through his eventual willingness to volunteer info, not because we probed. Both boys liked connecting with us via FaceTime more than we thought they would.
Two: I became a lot less concerned about playing time. When kids were in HS, I was silently obsessed with that. As others have said, support everyone on the field. If you can't handle being at a game while your kid is on the bench, then don't go to the games.
Go to every game you can. Don't cheer for your son. Approach it like watching your kid at practice. You're not gonna go berserk when they make a good play during practice; don't react that way at a game either. If you're somewhere private, though, knock yourself out.