Weave in themes. Use the major themes of your life as a way to tie stories together, connecting your past and your present. Aside from the central conflict, what themes have followed you throughout your life? A fondness for certain holidays, your fascination with a certain place that you visited over and over, a certain type of guy you've always fallen for, a rich spiritual life you fall back on again and again. Bring up the themes every so often to help form a cohesive picture of your life.
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.
Writing an autobiography for a high school or a college English class can help you gain a deeper sense of personal identity. An autobiography allows you to tell your story in a way that reveals truths about your values, goals and dreams. Though there's no exact science to writing an autobiography, you should include information about your background, major events that shaped who you are and any core themes in your life. Include specific examples to help readers understand your life history.