Combination of self-taught, and learning from photography boards. I have been casually snapping for decades up to 2003 when I got my first advanced digital. I found a photography website where I could post my pics, and receive comments and criticism from other, excellent photographers on the site. Though I was already a self-taught and somewhat experienced amateur, I learned probably 4 times more in a year or two on those sites than I had in the previous decades of shooting.
I've never really believed in reading books or taking classes for any 'artistic' venture...not that they may not be appropriate for some, but for me, art is in the heart and it must be discovered naturally to maintain one's own style and vision. You can learn the 'rules' but should know when it feels right to ingore or break them, and understand how to use them in your own personal style. Posting your shots for criticism is always a favorite for me, as it allows you to still post your style and vision, but receive objective criticism on what errors you are making or issues others will notice, and can then choose to fine-tune your style with those corrections in place.