It’s important to have a focus for your work so that you don’t get lost. A good way to develop an initial focus is to do some brainstorming and see where you have the most interest and energy. You can always expand on this initial idea as appropriate, or move on to other aspects of your life later.
Start with a blank sheet of paper and draw a circle in the center. Label the circle “me.” In diagonal lines radiating from the circle, jot down a few ideas for an initial focus. These could be as simple as “the years between five and eleven.” Or you might choose a thematic focus such as “interesting people I have known.” It helps to list half a dozen of these ideas on different lines radiating from the circle.
Now draw a line perpendicular to the line on which one of your ideas appears, preferably the one that attracts you the most. Say you wrote “interesting people I have known.” Write a subset of that idea on the perpendicular line. It could be something like “characters I knew in the Air Force” or “those who were inventors” or it could be the names of specific individuals. You can continue this branching process, using perpendicular lines that branch off your subsets, to generate ideas. By looking at the diagram over a period of a couple of days, you may get a better sense of where you would like to begin your memoir.