Everything that has a beginning, has a middle

I've been playing guitar on and off (mostly on) for the last 12 years. For the first 8 or so of those 12 years, I was a diehard metal/shred head. It was all riffs and licks and scales, and I hadn't the faintest clue what a ii V I was. About 3 years ago, I decided it was time to take my guitar playing a little more seriously, and made a concerted effort to learn some jazz... and fell flat on my arse. Hard. And that's when I realized a few things that were really, really, really important, and helped me along heaps

1) Know what intervals are and how they relate to chords and scales

The first gap in my knowledge was I didn't know offhand any intervals other than the root, 3rd and 5th. So I sat down with the major scale (G major, for example), and learnt what the intervals were. Then I extended that to all 7 modes, keeping in mind what the intervals were, what they sounded like, how they looked, and how each mode could be used to construct a chord using the 1st, 3rd, 5th and 7th interval of the mode. That's when I started to "listen" to the things I had only "heard" before, and things started to make sense.

2) Become intimately familiar with ways to play 7th chords, in different positions, across different strings, in all inversions

I had the good fortune of having some guidance from a fantastic jazz guitarist who plays out every night, in Singapore. He was kind enough to share with me his own learning experiences, and some of his own instructional material that he was compiling. Of these, what I felt was the most useful was the one that introduced me to playing chords in all inversions, across different string groups, in every position. I religiously studied that for awhile, until I was familiar with the basic 7th chords (M7, Dom7, m7, m7b5 (half diminished), full diminished). Playing this across different string groups, tackling them one at a time, and working my way through all the inversions, in about 6 months I had become able to pretty much play them on the fly as and when I needed to. The next step in the equation was to add all the colour tones (9s, 11s, etc) and extend this knowledge to altered chords. Knowing what chord tone was where in the shapes I was holding REALLY opened the gateway to understanding everything. After a time it stopped being a shape, and instead became a collection of notes, and once I understood how those notes were organized on the fretboard, altering a note here or there to produce the desired effect became cakewalk.

3) Get some basic understanding about chord progressions

My simplistic view of things is that everything can be broken down into its component parts. Looking at a chart for a jazz standard and trying to make sense of things 1 chord at a time was all good and proper, but that didn't really reveal the big picture to me. I needed a little more perspective, and that's when I started to learn a bit about chord progressions. If you've done 1 and 2 from above, by now you'd know the rudiments of scales, you'd know how they relate to chords, you'd know how to play those chords all over the place, and that makes it much easier to see how all those things are related to each other in the grand scheme of things. My own personal experience was that studying jazz standards was a great way to get your head wrapped around common progressions, as well as variations of them and reharmonization. And once you identify what key a certain portion is in, it's a good way to start thinking about what sort of arpeggios/scales/melodic ideas you can use over that. I'm still struggling with this, trying to find creative and musical ways to navigate through all the changes, or indeed, even within something as simple as a ii V I, but it does start to make sense after awhile

4) Play with people. Lots of people. Especially people who are better than you

I threw myself into the deep end and just started jamming with anyone who was willing to jam with me. Every time, it was an awesome learning experience, and it didn't matter whether they were guitarists or sax players or whatever. I soaked in whatever advice I could, and I tried to listen to what other people were playing as much, if not more, than I listened to myself.

5) Apply, apply apply!

This is really an ongoing phase but take steps 1 - 4 and just keep using them, and try and be conscious of it, at least in the beginning, until you have internalized it. It's a lot of information to process, and do it in bite sized chunks so that you can digest it all thoroughly. I really regret not having the fundamentals early in my formative playing years, because I had to unlearn alot of bad habits and resist the urge to fall back on comfortable clichés simply because I felt that I was good at them. Take all this knowledge, and apply it to anything and everything, whether it's jazz or otherwise, because really, there's no substitute for practice!

5.5) Listen, steal, analyse

Ear training really helped me out over the last couple of years. I used to rely heavily only tab, and my sight reading is pathetic at best (although I do try and work on it!) What really helped me in getting happy with the way my playing sounded was to listen to lots of music, find stuff I liked, figure out how to play it by ear, and then once I had copped a particular lick, phrase, or sound, figure out what I liked about it and how I could transpose it to different keys or apply it with different phrasing or note choices. I think this really helps you be inspired by all kinds of music, but at the end of the day, take all that inspiration and make it your own. It's cool to have a huge vocabulary of licks, but I think it's much more cool to have a huge pool of concepts that you can draw from.

That's sort of my little journey from then til now. Best of luck in your musical endeavours!