Think about the place where you grew up. Using as many sensory details as possible, describe the physical setting of your home, your town, your county, etc. What did you hear, see, taste, smell? Write about this for 10 minutes.
Think about your parents. Describe in as much detail as possible how they ended up in the place where you grew up, what they wanted, and where they came from. Write for 10 minutes.
Think about your grandparents or great-grandparents if you can. Describe where they came from, and how they ended up where they did, what they worked for, what you remember them saying to you. Write for 10 minutes.
Think about the greatest influences on you in your life so far. Are they familial? Social? Artistic? Describe these influences and how they have led you to where you are. Write for 10 minutes.
Think about your significant other, or your closest friends. How do your relationships with them affect you? How do you exist and act within these relationship contexts? Outside of them? Is the way you perceive yourself at all dependent upon these relationships? If so, how? Write for 10 minutes.
Think of your greatest hope or dream. Describe what it is, and why you want it so badly. Write for 10 minutes.
Review the brainstorming you have done. From the writing you have so far, choose the stories or details that seem most crucial to your identity, those that most shape who you are. Underline them. Use them as starting points for longer, more structured pieces.