Write out your life timeline. Start writing your autobiography by conducting research on your own life. Creating a timeline of your life is a good way to make sure you include all the most important dates and events, and it gives you a structure to build upon. You can consider this the "brainstorming" phase, so don't hesitate to write down everything you can remember, even if you don't think the memory will make it into the final version of the book.
Capture the spirit of the times. How was your story shaped by the moment in history in which it took place? What wars influenced your politics? What cultural events inspired you? Be sure to include a few important dates so readers can understand the sequencing of the events you are describing. Discussing what happened in the world at large during your lifetime is a good way to make your story more relevant and interesting to those reading it.
Develop a central theme, main idea or thesis that clearly explains the purpose behind your autobiography. For example, your theme might be about how you overcame obstacles to become a stronger person, or it might explain why a particular passion -- such as mountain climbing or rescuing animals -- is so important to you. Back your theme with details and background information about your life experiences. For example, you might explain that your dad is in the military, so you've had to learn how to adapt quickly to new schools and unfamiliar environments. Or, you might discuss what it was like growing up in a poor, single-parent home, but how your family was always willing to take in injured or stray pets.