My advice.
At the beginning of your first game brief lay down the ground rules, make them know that your in charge. Even if there is a large group or a stag do, if you shout at one of them and make him look stupid in front of his mates then you will be seen as in charge.
Pick up an old ball off the floor and physically demonstrate that it wont fit down the barrel, that will show them your not making it up to get more money out of them.
Give a short but very serious talk about lifting goggles, say about blindings/deaths etc happening in america. The adults may think its BS but the kids will be scared enough to leave there mask on all the time.
Work with your other marshals. As said, use hand signals (or radios if you can) to keep in permanent contact. As if one of you is fixing a marker/helping a punter the other marshal needs to know where you are. I always found a whistle a good idea to start and stop a game, and if people keep shooting blow the whistle in their face, works a treat.