Reading Campbell’s The Hero With A Thousand Faces was a real help to me in organizing an approach to writing fiction.
Non-fiction outlines are (for me) relatively simple. There’s a goal — some large technical exposition -- and there are details preliminary to this goal. The general technical area provides a context that frames the exposition. Maybe it’s data analysis using the Python Programming language: there’s a fixed, easily understood arc to what’s revealed and when.
When I first tried to write fiction, I didn’t have any useful guidance. I read everything I could on screenplays, because there’s a careful structure to movies. But screenwriting advice didn’t seem translate well to the more flexible world of SFF novels.
Campbell's three-part story with Departure, Initiation, and Return has been a gift. This creates a framework in which events must happen which leads to characters colliding.
There are, of course, critical joint and seams in Campbell’s view of mythological story-telling. Places where critical decisions are made and the story can evolve down a variety of alternative paths. This, too, is a wonderful help. It provides a sensible set of circumstances where the hero can make a wrong choice and suffer from that.