To write a story about your life, start with three sentences that summarize your life. Next, write about a crucial incident that shaped your story. When that is completed, figure out the details behind why you made the choices that led you down that path.
The three sentence summary concentrates on specific information about your life instead of a broad array of issues. These sentences are like a thesis or main structure of your story. One example is, "My parents always fought. I married a man like my father. I decided not to be like my parents." This exercise produces a micro version of your story without all of the details.
The crucial incident is any event that set you down a specific path. Start it with a line such as "I was just a child, but ..." or "It was the greatest single moment of my life" and fill in the rest. If there are multiple incidents related to the structure of the story, write out the details of each event.
Using the three sentences and the crucial incident as inspiration, think about the reason why you made the choices that caused the incident and how that affected your story. Write a few sentences with a statement such as, "I'd like to understand what made me choose a man like my father." Answering those statement gives you the purpose for writing the story and connects the first two exercises into a longer narrative.