When I composed, I heard my music played by the orchestra within days of completion of the score. No master at a conservatory, no matter how revered, can teach as much by verbal criticism as can a cold and analytical hearing of one's own music being played.
People who don't do jazz think it's black magic. But really, it's just a matter of getting used to it. It's fun to gamble. The trick is not to fall back on the things you've done before.