I'm not sure I can be bothered giving you a complete guide, considering almsot all DZ websites will give plenty tips, but i'll give you a couple pointers!
Basically, chill out. It's good to be scared but definitely not good to freak out. The most important thing is safety. I'm going to assume you're in the USA, in which case you need to be especially aware of safety as not all dropzones there will be that concious of it. Make sure you are given a jumpsuit that fits, a helmet, a 20-30 minute brief (for tandems, for AFF or Static Line courses you will need MUCH MUCH longer!), goggles (for high altitude jumps only, unless you wear glasses or contact lenses) and most importantly, you must trust your instructor. Don't hesitate to ask any questions, no matter how silly you may think they are. It would be pretty gutting if something went wrong on the jump and you had to regret not asking about or clarifying something whilst plunging to your death!
After safety comes enjoyment. You are doing a jump to have fun. It will probably be the most exhilarating experience of your life. Just go for it.
So long as you listen to your instructor and don't let your nerves get the better of you, you'll have an amazing time!