Memoirists often struggle with figuring out what to include. A memoir, by definition, is not a story of your entire life. It is writing on a particular strand of your life - a recurrent theme or issue or approach - or focusing on one particular era. If you are including everything that is happening, it will not work.
However, you also need more than just the key stories. What might otherwise seem like mundane details - how you make your coffee, or did during that era, or how it has changed over time - could lend a lot of real human feeling and connection to the reader. And everything depicted in the memoir can carry the feeling of communication, the sense it was all included for a reason, even if - especially if - that reason is not explicit or overt.
How do we choose?
We choose based on intuition, and then with a lot of help from our friends/editing crew. But it can help a lot to know that while the big events - deaths, enlightening moments, etc - have to be included, they also have to be surrounded by it doesn't really matter which daily details. Grounding the profound in the mundane is not just a "technique" - it is how we actually live our lives.
From True Perception, by Chogyam Trunpga:
We experience some shift or breakthrough in our minds in every situation, whether it is an experience induced by psychedelic drugs or a natural experience such as a personal dilemma, personal revelation, or personal tragedy. Then we turn some of these experiences into highlights. And often, one particular highlight becomes a crucial password in our lives, a turning point. “The first time I had that experience I felt fantastic! It struck me like a bolt from the blue!” But whether an experience is ordinary or extraordinary, every experience is regarded as a message. It is not like a telegram from Western Union, announcing that somebody died or got married; it is a message of the natural situation.For instance, I am revising a scene right now in my main memoir where one of my best friends at the time tells me a MASSIVE insight he has about my love life. My friend was - still is - hilarious and well-paced at delivering such messages, so the dialogue writes itself. But I can't simply plop the reader down in the middle of the dialogue. I need setting - me cleaning up our breakfast, him tipping back on his chair. Maybe he wasn't tipping back on his chair just then, but he almost always does that, and at that time, my way of avoiding the truth in any situation was to focus on things I could control, like dishes. So I ground the reader in my dishwashing, my anxiety about my friend breaking my chair, and my friend's casual ease at delivering one of the most powerful observations anyone has ever made about me. It all takes place in a tiny, shitty, kitchen/dining room in a post-college one bedroom apartment. Totally ordinary.
All of the richness of the details I am including communicate something. At the time, it meant nothing to me that I always washed dishes, and nothing to me (other than that it irritated me) that my friend always tipped back his chair and balanced it on the back two legs. However, those become objective correlative - a fancy literary term for extended symbols. Natural messages that come through the text without explanation. The tension between my dishwashing and his chair balancing is crucial for delivering the punch, though I say nothing overtly about it.
A balance of what is overt and direct needs to be counter-balanced with subtle, mundane life. Obviously we don't include all detail - but carefully choosing the details that are true to "character and time" is a strong way to embue what at the time may have seemed to have no significance with power needed to support your stories. Explore the details. Don't analyze them - you don't have to register all the details against Jungian psychology or interpret your past like a dream. Just feel out what is not only accurate to then and who, but also that moment.
What tiny details communicate the message you want to be expressing in that memoir moment.