In the three seconds it takes you to walk through a door and extend your hand to someone for the first time, that person has already made irreversible judgments about you. You send out hundreds of signals about yourself, and people read those signals and react to them long before you've had a chance to say or do anything of substance.

Camille Lavington is a communications consultant who commands substantial fees for teaching personal marketing to business people from corporate executives to mid-level managers. In You've Only Got Three Seconds, she shares her strategies for...