Actually when I was in the business I taught, a LOT (up to 62 students a
week at one point in 1977), and specialized in teaching improvisation to
both beginners and classical trained musicians on instruments other than
guitar. The procedure is the same for both novices and advanced
technicians: reduce the complexity of the chords and scales until the
player begins to "think" melodies spontaneously. Then slowly (obviously
more slowly for novices) increase the complexity of the chord changes
for each improvisational exercise.
If you would like to hear more details and their applications to
writing, lemme know.....mer