The simple answer is to play your instrument… ALOT, and practice, practice, practice. What you’ve listed that you are already doing is perfectly correct: get tab from the Internet, play along with your favorite CD’s, talk to other musicians. That’s how all the great musicians got to be that way. No one taught Coltrane how to be “Coltrane,” or Stevie Ray Vaughn to be “Stevie Ray Vaughn.” They just practiced alot, played whenever, and with whomever, they could.
Probably the best thing you can do is to play with people and share tips and tricks, it really does help you improve quickly. Unfortunately, you are probably like alot of us on this board, where playing an instrument has become a hobby which we have to fit around work and family, so finding time to play with a band can be pretty hard. But try if you can.
Here are some tips that I used to help figure out my ear. As far as single note intervals, the tip from masonite is what you’re always taught in jazz class: Identify what you don’t know based upon songs that you do. It’s very helpful. And if you’ve been playing guitar for two years already, you’re probably better at it than you think. For example, de-tune the A-string on your guitar pretty far. Then strike your E-string and based upon the sound of the E-string, strike your A-string and try to get it back in tune based upon what you “know” the A-string is supposed to sound like. That interval is the perfect fourth in masonite’s post. So, you’ve already started to develop your “ear”.
As far as getting familiar with chords and how they sound… I’ve played saxophone for years in all sorts of bands, so because of it I was very focused on single-note soloing, and was more “reactive” to the chords played by the rhythm section as opposed to figuring out the chords, per say. So, when I stated dabbling with guitar, I had a hell of a time with actually playing chord structure. One thing that I found useful was playing along with some jazz standards. Go pick up two books: 1. one of those Mel Bay books with every guitar chord fingering known to man in it, and 2. pick up a book called “The Real Book.” The Real Book is basically about 500 pages of jazz standards with the head, chords, and melody line written out. There are lots of different types out there, for example.
So, pick some songs out of this book that you know and find some CD’s with those songs (or find MP3s online) and start to play along. The jazz standards are great for the simple reason that they can be very hard, and there are lots of different recordings of them out there. Use the Real Book to see what chords are being played, use the Mel Bay book to figure out how to play the chord, and then play what you hear with the CD. I guarantee you, you’ll get frustrated and pissed off the first couple of times, but keep trying. It’s not easy work. Playing through some of the songs in the book will expose you to chords you won’t normally see in more mainstream music, you also get to see how the melody and the chords interact. And when you find a chord progression that you like, stop the CD and figure out what it is you like about it: remove and add notes to the chords and study how the “feel” of the chord changes; when playing a progression and the “feel” goes from a more “open” sound (a more major type chord) to a more “tense” sound (a more dissonant minor chord), figure out what notes changed in the chord to make the feeling change; then try it in a different key and see what it sounds like; after all that and you know what makes the chord progression work, mess around with it and try to create something new that you’ve just made up that you like better than the original. Now you have a set of chords that you know all about that you can use in different ways, styles, etc. What you’ve just done there is what every good musician that has ever played has done: find something you like, figure it out, and then make it your own. You’ll be surprised how fast you can improve your understanding of chords this way. The first couple times you do this will be quite hard, but every time you do another one it will get easier and easier because you have more knowledge and licks in your arsenal to call upon.
Unfortunately, there is no magic bullet. Just play your instrument alot, and enjoy it. Good luck.