Why are you writing your autobiography? Is it simply to help you understand your life or is it because you think it will make an interesting read, or both? Decide on the purpose of the story. Is it to help someone else get through a similar difficult time? Will it be quite draining for you to go over difficult periods in your life?
If you are hoping to have your autobiography published, think about your audience. What are the demographics of the likely readers? Will it tend to be people your own age who will recognize some of the history or will it be the public in general? Are you thinking commercially or personally?
Reflect on the events that had the most effect on you. The points in your life where something happened that made you change your lifestyle or move to another area or country. List the most important and work around them. Often writing an autobiography helps you understand your life and why you are where you are now and what made you who you are now. Ask yourself what the defining moments in your life were.
You need to consider what style you will be writing in. Are you planning to make it humorous or has your life been such that your story will be very serious? Or will it be a mixture of the two? Will it be a page turner and a story that people will not want to stop reading? Think about how you write, ask others what they think about your writing style.