First, good autobiographies establish facts and dates, and the authors also open themselves to readers. That is, they enable us to see their motives, which aren't always noble, and show us their pettiness and mistakes. If they show their weak side, we're with them when they write about their achievements.
Second, we need to ask ourselves: "Does this belong in the book?" The experience or anecdote may be good, but is it relevant to the theme and focus?
Here's an example of what I mean. I wrote a second book with Norman Vaughan called My Life of Adventure. Norman was one of those gifted storytellers and he had enough anecdotes for three books—wonderful accounts—but all of them didn't fit.
Here's my favorite. Norman played a minor role in the Battle of the Bulge in World War II. The German encampment was close by and one German soldier, wearing an American uniform, sneaked into the chow lines every day for more than a week. One day, however, someone bumped him and he dropped his tray of food. Inadvertently he yelled out something in German. They arrested the man. He confessed that the German troops were nearly out of food so he risked standing in line.
Norman was in the food line and saw it happen. It's a wonderful story, but it never went into the book. It didn't fit with the focus.
I include the emotions as well as the facts;
I leave out irrelevant material.