Find an old photo of yourself (preferably from your childhood) when, hopefully, you are engaged in some sort of family ritual that invokes a strong memory for you.
Observe the details of the photo. Are there objects shown that are inextricably woven with the memory of the activity that is taking place? Do the objects themselves conjure up strong memories of other situations or experiences? Be as detailed about the physical environment as you can. You can always weed out extraneous details later on.
Is there a strong feeling that is evoked by looking at this photo? Can you tease out this emotional state without directly referring to it? In other words, can you evoke it in your reader through your depictions that suggest the feeling?
---------------------------------------
Hopefully, though, there will be more to this experience than just the retelling of an old memory. Doing this would simply be nostalgic and sentimental, and this should be avoided.
The memory should be about something else besides just remembering the old experience.
Perhaps it might be about a way of looking at or perceiving the past.
Perhaps it might be about the kind of personal growth (disfigured?) that has ensued from that point.
Perhaps it might be just awe at the shape of a life that resulted from the remembered experience.
Perhaps it might be about the incongruity between the kind of person you are now and the experience that you remember.
Perhaps it might be about what a person with the kind of remembered experience that you had might do in a completely novel situation.
Perhaps the memory might be emblematic of something particular about one's ancestry.