I used to be terrified of doing any sort of dancing that wasn't a simple slow dance, as I just felt too silly and awkward. But I don't really know what happened... as I got older, I just started to give it a try, usually when pissed drunk at parties lol, and after awhile you realize nobody really cares what you look like. And truthfully, the girls actually love guys who get out there and dance with them and have a good time and if you can round up some of your boys to get out on the dance floor with you then all should be fine. Believe it or not, you look like less a fool if you are out having fun on the dance floor than the guys who stand around the edge looking awkward and not having any fun.
Just get out there and listen to the beat of the song.. it's usually just a steady bassy thump for most of the types of songs they play at dances, and just start moving your body to that. You don't have to go crazy "busting moves" but rather you can just sort of side-step to the beat if you want to (like Will Smith in the movie Hitch) and just move your hands sometimes. Try to throw some inconspicuous glances around the dance floor to get a feel for what other guys are doing, and just copy things that you see other people doing until you find something fun and comfortable for you. Most guys have a pretty repetitive, low-key dance style and don't go as nuts as the girls so don't worry about looking like a pro from So You Think You Can Dance.
Just one last thing - this might sound really silly and stupid to you, but maybe you will find it useful. If you can try to figure out some of the songs they might be playing at the dance (modern radio-clubby songs), you could try putting some of that music on when you are alone and practicing in front of a mirror or something. I know it feels goofy but maybe that could help you get some practice in and not feel like as much of a dork when you hit the dance floor unrehearsed.
Anyways, good luck bro. Even if you don't get into now I am sure you will start dancing more as you get older. Once you get into it, you realize how much fun you have been missing!