Although your memoir is about your life, it probably won’t be about your whole life. You are a complicated person with vast experiences and different ways to see the world. Yet in a memoir you must choose, basically, one lens through which to look at your own life.
Your “lens” will be determined by who you envision your readership to be, by the period of your life you wish to relate and by the incidents you choose as representative. Here are some questions to help develop and maintain focus:
Who am I writing for?
What is the underlying message of my memoir?
Are there pervasive themes of conflict and resolution that I want to explore?
Fiction writers are taught that the inner conflict of a protagonist should mirror or complement the outer conflict of the story. You might apply this same principle to your work. Does your life story reflect certain themes that you can identity and draw upon to develop a focus, such as a clash of cultures, overcoming hardship, life in a big family, the cruelty of war? What story do you want to tell? How does the inner conflict mirror or complement the outer conflict? For example, if you grew up as a white North American in China, your story may be partly about the contrast in values between the North American and Chinese cultures. How does what happens in Chinese society mirror or complement what is happening inside you as you experience these contrasts?
As you write, keep in mind inner and outer conflicts and choose the details from your life that help the reader see the conflict. I don’t mean that you should write only about the times in your life when you felt conflicted or in pain, but simply that every life manifests certain themes, as we struggle to understand ourselves, others and our place in the world.