For people in this thread, I strongly recommend Rob Fitzpatrick's book on how to write a book as a business, "Write Useful Books: A modern approach to designing and refining recommendable nonfiction":
Most of what they talk about is fiction, romance novels. No wonder it's still popular to be sold, I'm the wrong demographic, to me they're the generic rags with the generic tall strong man and falling woman on the cover. They give them away at the library and nobody wants them still.
https://www.amazon.com/Write-Useful-Books-recommendable-nonf...
Even though I'm not an author I found the advice very useful, it can trivially be applied to building and marketing any product.