I'm teaching myself to play through tapes and books. Most of the time I can pick out a tune I've heard either on a recording, or one that I can remember singing when I was a child. I have been finding that I need some written material, as I am not experienced enough to figure out which chords would be suitable for some songs. Also, there are some classical, jazz, Broadway, or old time tunes I have never heard before. ( And I have been playing mando for only four- going on five- months.) Anyways, we all have the rest of our lives to learn this beautiful instrument, so use all the techniques you can possibly find and do experiment! It will make your playing much more interesting and unique.
You are only young once, but you can be immature forever.