I don't write, but I have found several incredible sources for music theory--and by that I mean stuff like how do you create all the major scales, what are the basic chords that go with each of those major scales, what chord progressions are frequently encountered and why, etc.
You may already know all this stuff, or may not feel it's essential--but it's been a huge new world that's opened for me, and I think it's important as I learn guitar.
Try the following:
http://www.ibreathemusic.com
http://www.jazclass.com
the ibreathe site is focuse on guitar, but the fantastic materials there apply to all instruments, as does the stuff at jazclass.com, which by the way goes well beyond jazz.
Hope this helps.