He has a lot of clear advice.
For example, he says, "To engage readers in a story you need to limit the number of characters they identify with and care about enough to find out what happens to them. Pick two or three. We also want a discernable goal to the story, but not more than one, please, so we can follow the narrative arc from problem to development to solution. These aren’t rules set in stone, but general principals or best practices for storytelling."
I've seen a lot of unpublished manuscripts that lack a story goal, and/or have far too many main characters.