This is always true, but at AAU/YBOA nationals it is definitely worth thinking about before you get on the floor. The players will be fast and strong, they can take a lot of contact and will give a lot of contact. Don't let it get out of control, but don't blow the whistle every possession either. Let them play the game - but I guess maybe you already know that from your tagline
You definitely need to ref well off the ball, as that is where the trouble will really start. But don't be in too much of a hurry to blow the off-ball foul until you have a feel for how the teams are going to play the game. If you need to send a message, see the whole play and send the right message at the right time to the right player(s) - that includes the double foul if they get too chippy.