Show, don’t tell. Many of us have heard it so many times that we’re wary of telling anyone anything ever again.
If you’re trying to make the leap from prescriptive nonfiction to fiction, the biggest change may be the need to write, you know, a story. A story with scenes and characters and dialogue and a plot.
If your story’s a good one, the plot may be no sweat and the characters may well take care of themselves—the key is letting them evolve. But you need to sew it all together scene by scene, and that’s not always a natural adjustment for the nonfiction writer.