Everything happens for a reason. Nothing happens by chance or by means of luck. Illness, injury, love, lost moments of true greatness, and sheer stupidity all occur to test the limits of your soul. Without these small tests, whatever they may be, life would be like a smoothly paved, straight, flat road to nowhere. It would be safe and comfortable, but dull and utterly pointless.
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.
If your writing is atrocious, or if you just need some help getting your thoughts in order, consider hiring a ghostwriter or a professional personal historian. Celebrities do it all the time. There is also a software that allows you to type your answers into a template on your computer, thus solving the problem of less-than-perfect handwriting. Many people also choose to type directly into an online template.
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.