Masello's rule #43 is a complicated one, but the gist of it is: give subtext to your scenes.
To expand on that: a scene in a story doesn't simply have to about what's happening in the scene. It could also contain some sort of emotional or thematic resonance underneath. The key is to show how ordinary action is underscored by something not so ordinary.
Masello refers to screenwriting in this essay, so I'll give an example that William Goldman likes to cite of great screenwriting. I believe it's credited to Frank Capra, but I'm not sure. The scene is as follows:
A husband and wife are on an elevator. The elevator stops before their floor, and a pretty girl walks on. The husband takes off his hat.
The subtext there should be obvious, but in case it isn't, the point is that the husband and the wife are trapped in a failing marriage. Instead of showing them fighting, though, the scene shows them doing something normal. It's normal to take an elevator. It's also normal to remove one's hat out of politeness in many social situations. But by doing it in this situation, the tension in that tiny space rises faster than the elevator itself.
I've done this sort of thing in my own work. The Tangent Online reviewer of "Time Ablaze" (Analog, June 2004), for example, caught what I was trying to do in the story. The story is about a time traveler named Lucas Schmidt who has gone back to 1904 to record the tragedy of the General Slocum. He meets Adele Weber, one of the victims of the tragedy, and the two of them end up falling in love. But all of their courting takes place under the surface of their conflict.
In his review, Chris Markwyn said, "The conflict between Adele's urge to save her family and friends and Lucas's need to preserve history is what drives the story, but it is generally muted, giving the story a quietly pensive tone that works well with the historical setting."
That muted tone is exactly what I was going for. I never show their love developing explicitly, on the surface. Instead, I tried to infuse their everyday interactions with an underlying meaning, so that when Lucas finally does the unthinkable for Adele, she understands. If I succeeded, the reader comes away knowing that all the time, they were falling in love, simply through watching the two characters' everyday interactions.