You need to check the format. These tourneys will either be a best ball type, where your team records the 2 best net scores of the group, or it will be a scramble, where you play the best ball each shot.
If it's best ball, just play your game. Don't try to keep up with the other guys as they'll be better golfers than you. If you manage to post 2 net scores for your team during the day, they'll be ecstatic. Like others already mentioned, just be considerate of golf etiquette. Don't play slow. Don't stand in your partners' lines. Don't get too drunk before the tourney is over.
A scramble is a whole different animal. You won't be needed for your shot most of the time, but contribute two or three good shots and your team will be smiling. Work on your lag putting. Your team will likely have you putt first to get a good idea of the line. This only works if you're lagging it to the hole pretty well, so work on your lag(ideally leaving the ball 1-2 feet past the hole on each putt). Also, usually in these types of scrambles, the teams are expected to use everyone's drive once or twice. If that's the case, then work on hitting fairways off the tee. Your team will know they're gonna have to use a lesser shot for your drives, so don't try and blast it up there with them. Just get it off the tee and keep it somewhat straight. You hit 4-5 fairways and your team will be able to choose when to use that drive wisely and you'll be ahead of other teams where their D players are topping it/slicing it all day long because they're trying to get it out there 300+ like their A and B players.
Finally, and I can't stress this enough, don't take it too seriously. Golf tourneys for amateurs are supposed to be fun. Drink some beers with the boys, make jokes, and have fun. Every tourney team will be better off if all their players are enjoying the day rather than treating it like the US Open.