Set your stall out early, firm but fair. If they are behaving then you can slightly relax, let a few things go that in a tempestuous game that you wouldn't, smile, talk to the players, answer questions as best you can as long as they aren't incessant.. Enjoy yourself because one tackle could make a walk in the park game, the game from hell! If that happens, then thats time to earn your fee, always get the main protagonists, the fouler, the retaliator, and the one that runs from 30 yards to make things worse. Slow that game down, blow for everything, don't let that one niggly foul lead to WW3...
Don't be afraid of upsetting someone either, they started it, make sure you finish it!!! and smile!!!