I learned a bit from community classes and books and videos when I was growing up and just out of college. Then I moved to where I am now, and the school where I teach has ASL as a world language class. Two of the teachers are deaf. One of them taught a class at our local university so I sort of "took" the class...well, I went to it, but didn't tell the university so I didn't have to pay! (I didn't get any credits, but I didn't care about that. The teacher let me do it.)
Then I have started hanging out with other signers, kind of by accident or chance I met them. The rest is history. My skills have really improved mostly from watching interpreters at our faculty meetings and just chatting with deaf people. The foundation of what I got in class was a good starting point, but the human brain isn't made to learn language in a classroom, it's made to learn it by communicating! 
