I am in full agreement with Reed. I think the idea of changing your scale as
you change chords is ludicrous, in that too much information is being
processed while you are trying to make a melody. My tendency is to minimize
the amount of thought required. Recognizing ii-V-I's, ii-VI-V-I, etc. are
essential in minimizing the amount of thought required.
When I first began studying jazz, I frequently caught myself thinking as the
chord changes went on about "okay, I 'll play Dorian here and Mixolydian
with a #4 here..." and found my lines boring, very linear.
It takes a lot of time, and a lot of patience to create lines that are
coherent and beautiful. I am still not there yet. But also keep in mind, you
are your own worst critic and although you may not think what you are
playing is great, others may.
Try recording your practiced improvs. I have found a couple jems is a pile
of coal many times that I did not realize until playing it back.
Anyone who is interested should also try applying Zen philosophy to guitar
playing. There is a book out on the subject which I have yet to read, but
use a Beginner's mind when practicing. Don't plan your future, don't think
about your past. Approach the instrument as if you had just discovered it.
Anyway, I am off of my soapbox. I hope that someone may find this rant
useful.