What a lot of musicians, myself included, don't realize is that there are various ways to practice. The old "drill until you get it perfect approach" is the least effective because all your focus is on the physical aspect of playing. You need to hear what you are practicing so that you can absorb it.
Practicing slowly allows you to hear and correct the flaws in your playing. Slow tempos provide a great view of your articulation. If your articulation is sloppy your phrasing will be affected. If you can play slowly, faster tempos will become easier.
Hearing is a significant step in improving, no matter what instrument you play. The ability to hear is as necessary as seeing to a painter. Scales, rudiments, long tones are all necessary but taken to mind numbing proportions they can become mechanical and stiff.
When you practice you should have a musical goal in mind. The first thing is to get the spirit of what you are playing. It may be sloppy but it's the first step in learning to hear a difficult phrase or concept. Once you get the spirit of something the letter will follow.
Mental practicing should be part of your practice routine. The act of sitting in a chair and thinking about a piece of music has as much value as practicing for hours. Drummer Grady Tate uses this method all the time. He told me, pointing to his head "that I prepare here."
Metronomes and other devices are tools that should be used wisely. Musicians need to develop a natural feel for time. The goal of practice should always be to prepare you for that most important thing; The gig!
The groove continues...