Find Eric Gorr's book, and work on your own bike. Try to get someone more experienced to guide you while you work on your stuff. Also, read everything you can find about it and try to look over the shoulders of more experienced people while they are working. Try not to be annoying while they work and they shouldn't mind too much. I learned a bit by reading about it, some from common sense mechanics, and the rest from spinning wrenches (and I wasted a semester in auto shop in high school).
Reality check starts here:
Some people are born with an innate inability to understand anything mechanical. Typically these people buy their tools at Wal-Mart. If you fall into this group, and get confused shortly after finally remembering that you turn the TOP of the bolt to the left to loosen it, then you should befriend a person that knows how to fix bikes. Tool ownership is not a right, it's a privilege.