Let your students see you practice.
Just as we don’t want to put an unfinished performance in front of an audience, teachers want to walk into rehearsal polished, prepared. Ready.
But students need to learn how to practice, and maybe the best way is to see someone else do it. So I try to take a little time when the opportunity arises to practice in front of my students. Maybe just a minute or two of demonstrating how I would practice a problem spot. Maybe taking a few different approaches to a conducting moment. Maybe they see me rewrite a piece on the spot, working it out in real time. (The same goes for my composition students; if the opportunity presents itself, I’ll compose in front of them.)
That sort of live demonstration can give students a scaffolding for approaching their own practice more effectively, and seeing ways to make it more rewarding and productive.
It just takes being willing to be unpolished in front of your students.