How to Write a Memoir by William Zinsser

"My final reducing advice can be summed up in two words: think small. Don’t rummage around in your past—or your family’s past—to find episodes that you think are “important” enough to be worthy of including in your memoir. Look for small self-contained incidents that are still vivid in your memory. If you still remember them it’s because they contain a universal truth that your readers will recognize from their own life...

Remember: Your biggest stories will often have less to do with their subject than with their significance—not what you did in a certain situation, but how that situation affected you and shaped the person you became...

Here’s what I suggest.

Go to your desk on Monday morning and write about some event that’s still vivid in your memory. What you write doesn’t have to be long—three pages, five pages—but it should have a beginning and an end. Put that episode in a folder and get on with your life. On Tuesday morning, do the same thing. Tuesday’s episode doesn’t have to be related to Monday’s episode. Take whatever memory comes calling; your subconscious mind, having been put to work, will start delivering your past.

Keep this up for two months, or three months, or six months. Don’t be impatient to start writing your “memoir,” the one you had in mind before you began. Then, one day, take all your entries out of their folder and spread them on the floor. (The floor is often a writer’s best friend.) Read them through and see what they tell you and what patterns emerge. They will tell you what your memoir is about and what it’s not about. They will tell you what’s primary and what’s secondary, what’s interesting and what’s not, what’s emotional, what’s important, what’s funny, what’s unusual, what’s worth pursing and expanding. You’ll begin to glimpse your story’s narrative shape and the road you want to take.

Then all you have to do is put the pieces together."