What John Irving told an interviewer at Boston University about the most important quality in novels surely applies to memoirs too.
If you’re going to write novels, you need to establish momentum. The longer the novel, the more that momentum is essential. A novel must be more compelling, more urgent, to the reader on page 400 than it was on page 40. Two elements give you this necessary momentum. You must be able to develop characters; the characters must grow, and the reader must be growingly involved in what’s going to happen to these characters. You have to make the reader care about your characters. The second element is connected to the characters; the story must hold the reader’s attention—first, by inviting the reader to anticipate what’s going to happen; later, by having kept something a secret from the reader. You must allow a reader to guess what’s going to happen, but the reader has to be a little wrong. Note that I’ve said “going to happen” three times in this paragraph. That is where the momentum lies: always ahead of where the reader is in the book.
Of course, Irving said he isn’t interested in memoirs:
Most memoirs don’t interest me; I have no interest in writing one. When I do use things that have happened to me in my fiction (and not much of interest has happened to me), I always change it; I’m a fiction writer—I can improve on almost any so-called “true” story; sometimes making a story better in fiction means making it far worse.