1. Do you know exactly what you’re going to work on next? If not, search whatever learning materials you’ve got on hand for something to learn.
2. Next time you sit down with your instrument, don’t start by letting yourself wander aimlessly—instead, give yourself a moment to think and decide what you’re going to play, or what you’re going to work on.
3. Next time you make a mistake, stop playing. Immediately attempt the troublesome part again, at a slower tempo if necessary, and repeat this process as necessary to correct the mistake.
4. Are your practice sessions difficult enough? Or are you just repeating things you already know how to play?