[Andy]

Girls vs Boys game - Really apply advantage/disadvantage. It generally takes a lot less contact in a girls game to cause an advantage to be gained.

First 3-whistle game - Read up on the mechanics and rotations, let your partners know that this is your first 3 whistle game and ask them to have a thorough pre-game with you.
After all that is done and the game has started, remember to keep officiating the ball game. Don't concentrate so hard on where you are supposed to be on the court that you lose focus on the ball game. You will probably miss some rotations. Your partners will know, but don't let anyone else in the gym know.