The only way I do know how to play music is "by ear"...and often I would learn a song by listening to it in my car on the way to the party, and I play it live that night. I try not to always do that as my hardest thing is not the music or the playing, its memorizing the lyrics.

I love catching things on the fly, and for me it comes easy.

I wish, and I would love to learn a systematic way as Scottyee was talking about "chord progression" "blues progression" and other stuff that sounds so systematic and once you learn it u will be able to recognize it. Maybe one day I will dedicate sometime into getting to learn theory of music and how to read notes.