Jennifer Finney Boylan in Signature:
One suggestion I have for writers of memoir is that you should use the same rule to structure your scenes that you would use to decide when to arrive at, and when to leave, a cocktail party. That rule might be summarized: Come in late, and get out early.
Let’s say you’re invited to a party that begins at 9PM. What time do you arrive? Some folks might say ten o’clock, others closer to midnight, but almost no one would say to arrive exactly at 9PM. I admit that I’ve had a few friends who can be regularly depended upon to do just this, but let’s be honest: their exactitude is embarrassing. It makes me like them less.
Plus, being the first person at a party is mortifying. You stand around, watching your host take cheese out of the refrigerator. As Jimmy Durante use to say, “It’s mortifyin’.”
And in just this way, you don’t want to start your first scene — or any scene, for that matter — from square one. Don’t write the narrative equivalent of people who arrive at a nine o’clock party at nine o’clock. Arrive late—not so late that your reader (or your host) is overly confused. Arrive precisely late enough to be interesting.
Example: What’s the most commonly used opening sentence in stories written by student writers? I can assure you it’s something like, “Ring! Ring! Ring! said the alarm clock.”
More here.