Etiquette used to be:
When Bills are on offense - be quiet, sit down unless it's a big play or we're in the red zone
When Bills are on defense - be loud, sit down unless it's 3rd or 4th down
It's a younger crowd these days that doesn't mind standing for everything. I'd recommend getting either first or last row if you have elderly friends/family - at least with last row they can lean against the back wall the whole game