My teacher told to me:

4) When you can’t practice your cello, there are still ways to practice being a better musician. Let’s say you’re away from your instrument during the holidays for more than 3 days (the amount of time I think it takes for rust to really set in).

– Listen to music; any music, and pick out a lower line and follow it. If you feel the urge, sing along or create a harmony. This is most enjoyable in a snobby Studio City grocery store where it’s de rigueur to look like you’re talking to yourself because you have the bluetooth thing strapped to your head, but when you dare sing quietly, you get disparaging looks. Hee hee! My vocal teacher called people like that Soul Killers.

-Play arm cello. You ever do that? Take your right hand and put it on your left shoulder. There ya go. Portable fingerboard. It’s a common sight outside of competitions and auditions where there are no practice rooms to warm up in: a whole hallway of arm cellists. Plus, if you get all weird with your vibrato or extensions when you put bow to string, it’s an opportunity to clinic yourself without the liability of hearing the output. Oh, and you become aware of any thumb pressure you routinely apply when it’s your arm that gets the squeeze.

-Follow along. With sheet music in hand, follow a recording of a piece that you have not yet studied. Tap your foot and try to connect with the rhythmic aspect primarily. Wow. Illuminating.

– Visualize. As you fall asleep or before you get out of bed in the morning, imagine yourself playing whatever you’re working on from an observer’s point of view. Idealize your technique, smoothing out the kinks that may still be waiting for you when you return. Listen to the sound and marvel at how smooth, solid and easy it is. Imagine loose shoulders and thumbs, and breathe naturally as you observe this future version of yourself. Doing this sets a visceral goal that has more oomph to it than just saying “better” or “looser” or “faster”. When you vividly imagine yourself attaining a physical goal, it’s almost like your body will have a memory of doing it, which then helps you cultivate a feeling for actually making it happen.