If you're tackling something that demands concentration, music with a consistent rhythm and no (or incomprehensible) lyrics works best. Your brain can't help but pay attention to words you understand. Depending on the lyrics and what you have to get done, this can sometimes be more distracting than inspirational.
"Your brain is a prediction machine, making an endless series of guesses about what's going to happen next. When it comes to music at work, you don't want your brain to spend cognitive resources predicting what it's about to hear. Listening to constant, relatively unchanging music -- songs that don't have a lot of emotional peaks and valleys, or changes in mood -- has been shown to enhance some simple cognitive skills. Other research has shown that "low-information-load" music -- simple tunes without a lot of complexity -- have the strongest positive effect," explains Pasick.
If you're trying to be more creative, variety leads your brain down pathways of new connections between ideas and helps your mood stay positive. "Your brain thrives on predicting the future, so throwing some randomness into the mix can reward you with a surge of the pleasurable neurotransmitter dopamine," says Pasick.
Interestingly, whatever kind of musical effect you're going for, the benefits diminish with use. (You've probably noticed that without science -- after a while your favorite cardio songs just don't keep you going like they used to.) This seems to have particularly useful implications for dancers rehearsing for roles as well as supplementing daily routines with strategic song doses. Obviously you need to know your music inside out and be tuned in to all its subtleties. But to keep the emotional connection fresh, it might be best to put it aside for a while between rehearsals.