The first thing you need to do is learn the basics about a guitar. Such as scales, modes, chords and some music theory. This will help you know your way around the neck and increase your musical knowlege. You can either learn this on your own or get an instructor. Instructors are the best way to go. As far as deciding what to be, a lead or rhythm player, if you can do one you can usually do the other. And practice, practice, practice. :cool:
"Let that boy Boogie Woogie. Cause' it in em' and it got to come out." -John Lee Hooker-
There's no substitute for expeience. So get out there and break some strings on stage.