The interviewer's goal with that question is to see how well you can speak virtually unprompted under pressure. So, tell them about yourself. I usually tell them where I go to school, the jobs I've had before, who I live with, the general area where I live (i.e. it's proximity to the place of employment). Then I tell them some helpful facts about me, such as that I'm really neurotic, but that's partly good because it makes me extremely punctual because I'm so nervous about being late. As long as you don't lock up and tell them a few things about yourself that are relevant to the job, you should be golden. Just practice telling your friends or mom about your life and who you are.