No objections to anything anyone has posted, so I'll add a few:
Be willing and prepared to work as many matches as you can, and if you're aware of who the better programs are in your area, I would *not* work there during your first year. You'll probably see some really high level stuff if you do, and your inclination would be to think they're illegal (when they're not), and you'll set yourself up for a ton of trouble if you're not prepared to ref what you see (if that makes any sense).
If you can, try to watch some good officials work high school or pro during the nights you don't have matches, take notes on what you see, and feel free to ask them (probably the high school refs, as collegiate refs are much less accessible to fans than high school refs) about any questions you have. Good officials won't mind your questions if they see you're willing to learn, so use that resource if you can. While you're there, see if you can track the receiving team's lineup, and work on developing a system that you can use to determine all six positions on the court in a matter of maybe 2 seconds max. Master this, and you'll be way ahead of the curve.
Study your rule book and case book. Always have them on hand, and if you encounter a situation that stumps you while you're on the stand, look up the rule and reference and be ready in case it happens again, because it will!
Be prepared and willing to accept if you're wrong, and be willing to change your call if need be. But make sure if you do change your call, it's because you're wrong, not because a coach disagrees with you. If you're confident in your call, and coaches are arguing, be aware of the sanction scale and be prepared to use it wisely. Similar to a policeman with a gun, don't look to use it right away, but if you have to, you have to.
But most importantly, use resources like this forum to ask questions and gain feedback. It's helped me, and even though I'm fortunate that I often get to ref high level play, I am still learning, and I learn things from most topics that are posted here. We are all willing to support each other (well, except for one yahoo on another forum, but that's another story
), and we'll tell you when you do something wrong, but in a way that you'll learn, not feel bad about yourself. So don't hesitate to ask if you're not sure...we may tell you you're absolutely right too!
In short, learn as much as you can, don't stress too much, but do realize that it's not "taking candy from a baby" as many basketball refs like to think about officiating volleyball. As Jan said, yes, it IS an easy sport to do. However, if you actually want to be *good* at it...well...then you're in for some work.
Best of luck!