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.
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.
For example, let's say you wrote, "From the age of ten, I knew I would become a concert pianist." What specific event triggered this determination? Can you describe that one event in a paragraph or two, using all the senses available to you—sight, sound, taste, touch, and smell? Using all five senses will help readers imagine the moment as if they were present with you. This vicarious act of reliving events arouses more emotion in readers than simple summary. and if you can master it, you are well on your way to writing an autobiography! Sensory description: The narrow plank felt warm and smooth beneath my bare feet. I ran its length in three strides, arms extended out from my sides for balance. At the end I took a weightless leap into eighteen inches of space. I caught a barely-there flash of metal just before I landed hard, all my weight on my front foot. Then pain like a red-hot poker jammed through my arch, and the gleaming tip of a three-inch nail as it emerged through the top of my foot. Summary: That day I jumped on a board with a nail in it and it went through my foot.
Do you remember any other challenges you had to overcome that relate to each main point in the story? Did you move? Were you ill? Did anyone close to you die? Did any of these people or events affect the choices you made during that stage of your life? Do you remember any amusing or embarrassing incidents related to this success or failure? What high points and low points do you recall? Was a specific holiday or celebration memorable? A specific meal or car ride?
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.