The key was that he figured out how to set the range of tones to fit the image. There would always be at least one place in the image that was pure white, and one that was pure black, and every tone in between. He used all of the potential tonal range for each shot. For which he was often criticized for not making "real images." Not unlike the criticism aimed at HDR today. The problem isn't the process; it's in people who use it without understanding how to control it.
Not formal classes; just other knowledgeable people.
Mrs. Yehren doesn't know an f-stop from an EV, but she takes remarkable images:
What matters is an eye for images. She just learns what the camera can do. I tend to intellectualize things. Different approaches, but both work just fine.