It may help to identify the reading level of the ideal reader of your book. You can determine the reading level based on the grade level of your ideal reader. If you account for ESL readers, you should aim for a grade 6 or 7 reading level. If you are writing for a higher education audience, you may write at a grade 8 or 9 level. You can use the Hemingway app to determine the reading level of your draft, or other online reading level tools.
Create an outline or a graphic organizer of the major topics and ideas you want to cover. For example, you might make a time-order chart -- a chart with event blocks to organize events chronologically. Or, you might draw a cluster web -- a diagram with connected circles -- to divide your autobiography into sections, such as one for relevant background information, one for life-changing events, one for special memories and one for goals and dreams. Focus on reasons why specific events, situations and circumstances were important to you and how they made you feel.