Many of us have a commute that we'd rather be shorter, but what could be looked at as a waste of time can easily be turned into a worthwhile mental exercise. Fill your iPod or whatever flavor MP3 player you like with fun podcasts, dictated lists, and other audios that are a bit above your speed range.
While the tracks are playing, try mentally stenoing the words as they're spoken. You may find that this increases your speed when you go back to your machine and start writing again. A variation on this method would be to tap out the words with your hand or hands (only if you're a passenger -- 10:00 and 2:00, people!) Lap-tap the alphabet, numbers -- whatever comes to mind.
Or say you're in a boring meeting. You may not be able to get full lap-steno action without your coworkers noticing and giving you the stink eye, but why not bring a notebook to the meeting and jot down the steno outlines of words that come up during breaks in conversation or take down some notes too. Hey, it may even cut down on coworkers' requests to get your notes photocopied for them because they weren't paying attention.
Another way of getting in good practice is to review well-written paper steno notes while on the go, as recommended in this blog post by Stenonerd. I've said it before, and I'll say it again, but reading steno really helps our brains associate a good steno outline with the word it represents. Happy mental steno, all!