The best professional-services companies understand that their people are their only products, and that strong performance requires getting top talent to act instinctively in ways that always promote the company's strategy. A new study by Bain & Company finds that the service sector's exemplars put three leadership principles into practice: they align the goals of both stars and star-makers with those of the firm; they micromanage the culture, not the people; and they build upon partnership ideals, even if their firms aren't formally organized as such.