While you might not remember every detail about a certain event, I guarantee someone who was there does remember. Asking family and friends for ideas or details of a certain situation can give you a completely different perspective of the event or time in your life. That perspective might prove to be invaluable in your writing. Be prepared; once you get a group of family and friends together to reminisce, you will be shocked at how quickly the ideas come and how one idea can spark another and another and another.
Be revealing. You don't have to be explicit, but it's important to reveal truths about yourself and your life in an autobiography. Don't let the book become a list of your accomplishments, with all the negative material carefully kept under the rug. Present yourself as a whole person, sharing talents and flaws alike, and your readers will be able to identify with you and hopefully root for you as they make their way through your story.
Show, don't tell. Engage your reader by showing them a specific process or scene, rather than narrate directly to them. For example, write a scene that shows the reader how you discovered your mother’s letters from her family in Poland after her death. This will give the reader key information to help move the story forward, without telling them in a long, uneventful passage.
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.