New ref...Scared to DEATH!!!

[swmoref]

I need some good solid advice on my first "offical" game, Jr. High. I have done many "unofficial" elementary games in the past 6 years, but this is my first after passing test and getting "the real thing". I am looking forward to it, but have to admit I AM SCARED! What do I need to concentrate on to start with. My first 3 games are before any rules meetings or mechanics classes. Help PLEASE.