Please read my other post about open-ended questions.
"tell me about yourself"
Split between personal life and academic life.
Tell them about your hobbies, what you like to do for fun, how are your friends, what do you do w/ your friends, how is your family, what are your interests besides medicine, college you went to, how was life growing up, any remarkable incidents that changed your life, etc.
Academic life: Tell them about your classes, ones you loved, ones you didn't like as much, classes you thought were interested, teachers you've admired or helped you a lot along the way...
USE your imagination.