The most effective way I've found to motivate and engage the dancers I work with, has to do with being able to accurately identify the moment when they become familiar and comfortable with a certain way of working and thinking, and shift away from it. But you can't just shift for shift sake, it has to be a genuine evolution of what they know so far. 

Dancers authentically challenged and intrigued by what they're working on, will give it their hearts and souls.