The rules of writing a memoir are much less relaxed if the only people who are going to see it are your immediate family or a few close friends. It can be as informal as a handwritten notebook or a collection of audiotapes that you fill with anecdotes whenever inspiration strikes. There are no right or wrong answers in this approach because the readers are already fans and curious to know more.
If you want to take your life story to a broader platform, however, the first thing a publisher will want to know is how the material will resonate with prospective buyers. While celebrities or individuals who have survived extraordinary circumstances can usually find a market, workaday people have a tougher time of it because no one has ever heard of them. For an editor to want to publish your memoirs, the material either needs to have a distinctive style (i.e., humor), capture a unique time (i.e., Tiananmen Square 1989), or speak to a specific group (i.e., teen mothers).
Whatever your objective is for the final product, the point is to have fun and push your mental margins in recalling all the things that made you who you are.
An autobiography starts with an outline. If you're going to embrace a chronological style, the easiest way is to set up a three-act structure in which you divide your life into thirds; i.e., from birth through your 20s, your 30s through 50s, and wrapping up with where you are now.
Another approach might be to spend the first third of the book discussing your ancestors and then segue to how their experiences shaped your own choices about work, family, politics and lifestyle.
If you take a thematic approach to your story, the structure will either focus on the beginning/middle/end of one specific incident (i.e., a life-threatening illness) or take on the characteristics of an anecdotal anthology in which related stories are grouped together in their own chapters (i.e., "Early Jobs", "Romance", "Road Trips").
Once you start writing, your chapters can be worked on in any order and you'll often find that one memory will trigger a flood of others that you had previously forgotten.
To help you get started on your book of self-discovery, there are a number of excellent resources. Books such as Barbara Ann Kipfer's "4,000 Questions for Getting to Know Anyone and Everyone" pose questions about family and friends, spirituality, philosophies of life, the workplace and childhood. Margaret Tiberio's "The Book of Self Acquaintance" is an actual workbook for you to respond to questions about coming of age, relationships with family members, dreams, career choices and fears.
There are also genealogy software programs such as "Personal Historian" that offer creative writing prompts and assist in putting your life experiences into a cultural and historical context.
Enlist family members and friends who have known you for a long time to fill in some of the blanks and jog your memory about shared adventures. Troll through family albums; this not only conjures up more reflections, but you may also want to use some of the images to supplement your stories.
Last but not least, embrace a light, conversational tone in your memoir writing. This will make it fun and approachable for your readers and make them feel as if you're chatting about the past over a cup of coffee.