Most of us assume that success will lead to happiness. Shawn Achor, founder of the corporate strategy firm Good Think, argues that we've got it backward; in work he's done with KPMG and Pfizer, and studies he's conducted in concert with Yale's psychology department, he has seen how happiness actually precedes success. Happy employees are more productive, more creative, and better at problem solving than their unhappy peers. In this article, Achor lays out three strategies for improving your own mental well-being at work. In tough economic times, they're essential for keeping yourself-and your team-at peak performance.