Well you could try to find other musicians to comprise your own vision for a band or you could join an existing one.If you want to start from scratch,it would be a good idea to write some material first and then seek other members so they will know the direction your heading musically.Music stores usually have a bulletin board with alot of musician and band personals.Taking out a small ad in the paper isnt a bad idea either.I found a former band through the paper.If you want good mature musicians to work with in a band,you must have a mature ambition and realistic circumstances.Dont ask a phenomenal drummer/bassist/singer to come try out if your playing a squire bullet through a drive practice amp,and dont ask a novice drummer/bassist/singer to try out and play demanding technical music.
If your looking to join an existing band then just keep an eye out at your local music store bulletins,paper and listen for word of mouth from friends.Lots of music stores also have an open mic night or somthing to that effect where other musicians can meet and collaborate.
Good luck!

Later! \m/