Transcription means listening to music in detail and copying it by ear. Most jazz musicians at some point learn whole solos by ear; some memorize them directly, and some write them down. It doesn’t have to be a whole solo. It could be a tune or a phrase that you like. But the point to spend time regularly going directly to the sound, not notation, to learn the language. Listening in detail is the most essential skill in playing this music. Remember that the process is more important than the product. In other words, don’t judge success by how many bars you transcribe, but the time you spend trying to do it. Also make sure you pick a solo that you really like, since you will spend some time with those notes.

Sample Piano Transcription (Download PDF)
Here is my transcription of one of my favorite solos by one of my favorite pianists, Bud Powell, from the recording Sonny Stitt, Bud Powell, J.J. Johnson—Prestige Original Jazz Classics. I learned to play lines by transcribing solos like this one, working them up to tempo with a metronome, and finding phrases that I liked which had strong harmonic implication. I would actually circle them on the page. I then practiced those phrases in the other keys, which helped my ears and my ability to finger things on the fly.

Jazz Pianists You Should Know (Download PDF)
Here is a list I compiled some years back of some of the most important jazz pianists through the history of the music. Obviously are many others who are not listed, or have become known since then, but this list contains most of the important historical influences.