Don't Panic!
You're probably going to miss a lot of stuff at first. You'll see something, you'll think about it, try to recall what the rule is, and then finally realize that it was a foul/violation/whatever. But by then play has moved on. Get it next time. It just takes a while for everything to become automatic. So have some patience with yourself while you're learning.
Your partner is your only friend on the court. Learn to work with him/her. Always make eye contact before putting the ball in play. If you need a quick word to make sure you're on the same page about something, have that quick word.
Use that "game awareness" you developed as a player to your advantage as an official. Know the time, score, foul count, etc. Use your knowledge of offense and defense to help you anticipate the play. Then you can narrow your focus to seeing what is about to occur.
Blow the whistle with authority. No matter how unsure of yourself you are as a new official, do your thing with confidence. Fake it if you have to.
Don't be afraid to admit when you make a mistake. A simple, "Sorry coach, I kicked that one." can defuse a situation faster than any other bit of game management I've ever learned. Just make sure you don't kick very many
Call your own lines. Call your own area. Don't be a ball watcher.
Slow down.
Oh, and one last thing...
Slow down. Then slow down some more. Once you can do that, slow it down just a hair more.