Once you have taken a look at your own life from an outsider’s point of view, you will be able to select the most interesting elements from your notes to establish a theme. What was the most interesting thing you came up with in your research? Was it the history of your family and your region? Here is an example of how you can turn that into a theme:
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.