Some suggestions?
My personal favorite is a book by Arnie Berle called "Theory & Harmony For The Contemporary Musician". It's been a while since I read it front to back, so I'm not sure how much introductory theory it goes over. One may want to look into a beginner's music theory book, one that at least covers the circle of fifths, intervals, why and how chords are formed, tension and release, etc. (though I believe much of this is in Berle's book). The book goes more into modern jazz theory and will help in learning more advanced chord structures, various progressions you'll commonly find in standard jazz songs (and certainly any rock, pop, or blues song), and much more. Armed with this knowledge I'd hit the real books, as I stated earlier in this thread somwhere, and (starting with simple songs) work through the progressions, any bass lines that may be there, the chords to the song, listen to different recordings of these songs and transcribe what you hear the artists improvising (or the original melodies too if they've altered these any!), and I'd also improvise some of my own walking lines and phrases/riffs. By the time you finish this (which is really a lot more fun than it sounds on paper) I'm sure you'll have a thorough understanding of the song inside and out. Take what you've learned there a move on to another song, keep going til you can start to fully understand more and more complex songs throughout the books.
I'll stop here as this is where I currently am in my musical journey. Before me lies a book I'm currently looking into, "Arranging for Large Jazz Ensembles" by Dick Lowell and Ken Pullig, and on my computer I have open the real book in bass clef. The point of the last sentence is to say that once you've gotten to this point it is only the beginning of the real musical journey! From here lies still endless amounts of knowledge to be gained and internalized, and what you decide to learn from this point on is what will make you your own musician. Shaping your own musical style and sound, and separating your music from that of anyone else's.
I love the video, that I will post part two of, of Jacob Collier's interview. If you listen to his music, it's clear that nobody else sounds like that. But, hearing him talk about himself and his musical upbringing instills in me a belief that, though many may argue with it, nobody is truly special. It's clear Jacob has just gone through the basic steps of learning music (much like those, including his pal Herbie, before him and those who will come after) and is now at a point where he's actively pursuing the knowledge he feels would be of interest to him in adding to his own unique "pallet".
Isn't conversation like this delightful?
Edit: I'll add that this is, to the best of my understanding, what Mr. Berlin would describe a self-taught method. I highly recommend finding a college educated jazz musician to help you understand and internalize what you are reading, seeing, and hearing along your path, as well as to help direct you through songs in the real books, and also recommend more literature that's out there for you to gain from. This is what I've done and would be nowhere near as far off as I am without their guidance and support.