Make a timeline. Draw a chart on a piece of paper and divide the chart into columns. In each column, put the year or your age. For instance, start with the year you were born in the first column and each subsequent year in the following columns. You can also choose to divide your chart by decades rather than individual years. Another way to divide your columns is by using ages instead of years.
Pull out the key events of your life from your timeline. A key event is one that held some life changing power over you; it changed your life in some way. Choose one of these key events and freewrite about it. At this point focus on capturing the details and evoking important people and place--don't worry so much yet about what it all means or whether it is worthy for inclusion in your life story. As you attempt to vivify more and more key times in your life, the real unifying themes of your life--which are not always the ones you'd want them to be--will make themselves known to you.
Make a list of favorites. Far more than our ancestors did, we identify our and define our personalities with favorites. Start with listing all of your favorite books, movies, and music. List your favorite hobbies, your favorite chores and your favorite jobs. Write out as many favorites as you possibly can. Use these lists to spark a story. Favorite things are centers of interest and energy (and conflict!), and can be a useful alternative to simple chronology as a way to organize your life story in writing.
List all of the firsts in your life. Some ideas would be your first car, your first job, your first boyfriend/girlfriend; the list is never ending. Again, as with the favorites, use this list to generate ideas for life stories. Remember to add lots of detail and emotion to your story.
Browse through your families' photo albums. Old photos are a great way to find life stories to write about. Make note of the places in the photographs, and write stories about these places. Look for people in the photographs that you have lost touch with, and write about whom they were and what they meant in your life. Find a single photograph that moves you and play out everything you can remember about in writing--the people, places, circumstances and aftermath. Maybe you can uncover why this photo has more meaning for you than others.