For Students Who Struggle to Practice
In general, I practice hours and hours a day. Getting good at Jazz is all about getting good at practice. Practice literally becomes a meditative act, and something that transcends all else in life. You have to be the type of person who gets separation anxiety just having to put down your instrument for even a few hours. Practice is so important that Jazz great Sonny Rollins actually quit playing for some time at the peak of his career just to have time to go out and woodshed under the Williamsburg Bridge.
This said, there are a few important things to understand: First, consistency is most important. Believe it or not, 5-10 minutes a night of consistent practice will actually work more than going most the week without practicing, then cramming all night or day before the lesson. This is in part because it takes time for things to sink in. Cramming does just about nothing for muscle memory and development, and since in music over learning is learning, just sitting down at your instrument for a couple hours one day a week isn't really going to do much to turn you into a confident performer.
So, what it the best way to practice? First, you really want to have a clear picture of what you're working on. Consider your teacher a type of performance coach who teaches you how to practice. Do not pay to take a lesson without leaving with a clear idea just WHAT exactly you have to practice and how you're going to practice it. Sure, there are lot's of neat and cool things your teacher can show you, but in the long term, its all about preparing you for the week of study ahead.
Lessons should always result in two things:
Related to this, be wary of teachers who lack focus and provide very complicated homework assignments as if the lesson has a million different points. Remember, even a simple set of just a few repetitive exercises may require hours and hours of practice to get to the point that the marks are reached. Good teachers don't bury the main points of their lessons: they enforce and reinforce them. Furthermore, good teachers set goals their students can accomplish then build on those successes. They don't overwhelm their students with unattainable goals from the get go.
So, here's a new approach to thinking about your music studies: A music lesson isn't necessarily a place to learn stuff. It's practice training, then you come back to the lessons and clarify stuff, get more practice training, go home, and work on stuff some more. The real learning should occur between the lesson. If you've been taking lessons for years and haven't been making any progress, that's where the problem is: You're looking in the wrong place for the progress.
By the way, this concept is not my completely original idea. Check out articles around the web on flipped classroom learning!