Vargas is absolutely correct. Networking is the way to go. Get your face out there as much as possible. Talk to the guys/gals in the band and let them know that you're looking for something. They may know some other musicians that are looking for what you offer. Be polite, well spoken, and courteous, and you'll get a bunch of leads.
Research your area to find out if there are any resources available online for you. For example, my area (Central Pennsylvania) has 2 wonderful resources, PA Musician Magazine and Rockpage. PA Musician is a free monthly paper that supports the unsigned music scene and provides free classified ads for musicians looking for bands and vice versa. Rockpage is our own online version of that, where musicians (and fans) congregate online and talk shop, set up shows with each other, buy and sell gear, and look for like-minded musicians for our projects.
I can't stress enough what a pair of great resources they are. I've developed my subbing network through Rockpage, and sub for about 5-8 bands when needed.
1) tell everyone you know who plays that you're looking for a gig.
2) go to every show possible for the kind of music you like and want to play.
3) take every gig you can when called.
4) do #1 & #2 you're whole career and do #3 up until the point where you have a minimum fee you'd like to make at each gig.
If you have any friends that play instruments, offer them to jam session with you. Jam with some musicians and see what happens. 95% of the time you'll find that you guys have some musical taste in common and once you have that, you have a band.
I noticed its just being at the right place at the right time. you can't really expect to find a band with the exact kind of music you like. Have an open mind. Its working for me. Network a lot too. Get your name out in any way you possibly can. One day someone will see you and that will be it.