I got into sound engineering when the leader of the band (and owner of the PA) told me he was tone deaf. I figured I needed to protect myself. Anyway I took a one-day workshop at the local folk music society and after riding shotgun for two concerts I started doing them on my own. The folk society held concerts on Friday and Saturday each week so there was ample opportunity to practice the craft and learn on the job with a variety of styles and band configurations. If you have such a society nearby, then offer your services to them. The pay usually isn't much but the experience is priceless. If you don't, then look for venues that sponsor open mics/stages and again offer your services. These might not pay anything, but the experience is invaluable. I'm now teaching the sound workshops which have expanded to six days along with the number of sound systems in use at the society and I can't agree more with the previous poster who said, "Use your ears" and be sure to protect them too.