Hi there,
It sounds like you need to start by brainstorming.... ask yourself what has made you who you are today?? What life experiences, whether personal or professional, from all phases of your life? What DO you honestly see as the key aspects you'll bring as a member of the class? Honesty is key here, especially as you begin the essay process. You'll want to brainstorm everything you can think of, then review and choose some key traits or experiences to share, then work on an essay outline.
An MBA Admissions Consultant can help you with the process of drawing out your unique experiences, and providing feedback on your outlines and essays as you work. I definitely encourage you to get feedback throughout the process.
Let us know what other q's you have, and good luck.