Some of my students have come into their lesson this week, saying "Sorry, I didn't have much time to practice. I was really busy." Well, that just sums up everyone's life these days, doesn't it?
There are several ways that you can practice music when you are busy. I've already touched upon speed practicing.
Another thing you can do while you are in transit or while you are working on your schoolwork is to listen to recordings of either you playing your pieces and/or someone else performing them. I was working full-time in an office while I was preparing for my ARCT in Piano Performance from the Royal Conservatory of Music. Practice time, while working all day and living in an apartment was quite limited.
During the day, I popped in CD's of of piano repertoire into my computer and plugged in my earphones. Even though I was busy writing articles or sending out correspondence, some part of my brain was listening to my pieces and dissecting them. I would also listen to them on my commute home.
Sometimes, I employ this technique now with my Japanese language studies. I'll listen to our class recordings while completing my studio paperwork. Or, I'll listen to recordings of my students' pieces to refresh my memory before heading into lessons.
Another thing I did frequently was scorestudy, that is, to study the musical score. At lunchtime, I would I would sneak off to a quiet corner for five to ten minutes after eating to frantically tap out the complex rhythms in my pieces.
The third idea is courtesy of one of my students and applies for to music theory and ear training. It took her a long time to memorize her Circle of Fifths. I was impressed when she told me that she set the Circle of Fifths as her iPod wallpaper. "I had to look at it each time I unlocked it," she told me. As far as ear training and music vocabulary go, there's an app for that!