When I first started writing fiction I read a lot of books about how to write. How to write attention grabbing stories. How to engage emotionally with the reader. How to keep the story moving forward. The inciting incident. The danger of excessive adverbs. Why you should show instead of tell.
I’ve read widely enough to have a fairly well developed sense of taste. I know when something’s really good. I know when something’s bad. I know when it isn’t quite working.
The difficult part though is knowing what needs to change, and how to change it.