This short book written by Peter Rudin-Burgess is licensed CC BY. It is packed full of information describing a method of solo play where you are your own Dungeon Master as well as the protagonist Player Character. Although the book is targeted at OSR the techniques described can also be used by any Game Master in any game.
This link takes you to the book’s page at DriveThruRPG. The book is reasonably priced and Peter also includes the full text in the previews. He says, “I wanted anyone interested to actually see exactly what they are getting and the logic behind the design decisions I had made. ”
The book is nicely laid out with pictures and tables in the style of RPG manuals everywhere. Recommended. I plan on following this method while taking notes to develop narratives for short fantasy fiction.