Welcome to the crowd!
My favorite thing to tell new officials is to remember to have fun. When it quits being fun, STOP and GO do something else.
Watch as many experienced officials as you can. Read the rulebook, then read it again; now read the casebook, and try to relate one to the other.
Shut up and listen; your fellow officials will be more than willing to give you advice. Use it when it's given; too many people say they want advice, then when it's given, they ignore it and go on about their business.
Keep that whistle out of your mouth; after a year or two in the saddle, then you might want to carry it in your lips, but leave it out until then. If you work umpire, get a finger whistle. Most umpires I know rarely ever have to blow a whistle, but it needs to be there in case.
On our website, I have the Louisiana Football Officials Mechanics Manual that you may find to be useful. Go to
http://slfoa.tripod.com
Good Luck!