How to Improvise on Piano: Learn How to Approach, Develop and Master the Art of Piano Improvisation

I would recommend making your way through the Alfred books and learning to read music. It is your ticket to learning more pieces and recalling ones you used to know. Also I recommend getting a teacher. I taught myself a lot of bad habits and gave myself tendonities early on. The book How to Improvise on Piano is pretty good, but you still need to be able to read music at a rudimentary level in order to read it. Good luck!