Motivating employees to higher levels of performance is a challenge most leaders. Often people are motivated to do things simply because it feeds into the story they tell themselves. For example, your star performer regularly exceeds your expectations because she tells herself that she is the kind of person who impresses others, or a team member triple - checks a document because he is the kind of person who doesn't make mistakes.
You can fuel internal motivation by understanding and supporting these stories. First take notice of what kind of person your employees wants to be. Then articulate how what you need done fits into or even enhances that image.