Lessons had major chunks devoted to learning scales, and a variety of patterns involving scales, ascending and descending on my trombone. The goal was to be equally fluid in playing these scales and patterns in all 12 major and 12 relative minor keys (the kind most of us get in K-12 music), along with other minor scales and all modes (scales most of you don't need to know about). Oh yes, toss in arpeggios (going up and down chords) in all keys. That sounds like a lot of fun, right? (By the way, the same is true of my voice lessons, which for 28 years have started out with 10 to 15 minutes of exercises).
This is learning to speak a particular language, the language of jazz. Because once these patterns are automatic, the creative part of the mind can weave them into longer and longer improvisational performances. If you run out of ideas, they provide a fall back. When I face a problem in musical performance (largely vocal now), I think, "Trust your technique."
You might say, it takes passion to stick to this and I would agree, to a point. But there many amateur musicians who are very passionate about music. No matter how much passion they have, they lack the skills to excel. Their passionate emotions often make them simply sloppy.
Learning skills until they are applied automatically, almost unconsciously, is a key to being able to utilize passion. Paradoxically, it is that disciplined approach to learning that produces greater creativity than does undisciplined eruption of thought.
Go to Aebersold's site at www.aebersold.com and you can find his way still includes memorizing songs, another really un-passionate thing. And while I haven't seen him in decades, I notice his volume "Jazz, Anyone Can Improvise" has a CD volume, “Learn to Improvise in Every Key, Major and Minor."
I think his lessons would be very familiar to me after all these years. As one of his site's notes say, "Pick a different key each day/week/practice."