I've been reading Marc Sabatella's "The Harmonic Language of Jazz Standards" to help me better understand the harmony behind standard tunes. If you know any theory at all, there's going to be some review, but he's filling in plenty of gaps for me, as well as providing unique ways to look at harmony that are of special benefit to jazz musicians both for understanding chord progressions as well as learning tunes quickly and eventually being able to play melody and harmony by ear, without ever having seen a lead sheet.
Now, I'm nowhere near there, but the book works on many levels and is extremely well done.
What I'm working on right now is playing solo versions of tunes and keeping smooth motion in the bass. Marc points out that many chord substitutions happen for this reason. So for now, I'm focusing on the bass notes themselves, rather than looking for a good chord grip below my melody note. Only after I get the highest and lowest notes down do I add other tones in between.