Another necessity for enriching stories is character development. Often we think characters would (or should) act in a certain way with another character. I’ve heard that doing character interviews is supposed to help–finding out favourite ice cream flavours, um, and stuff. You can tell I’ve never interviewed a character before.
But another option is to free write a scene for your characters within the world you already created for them. For example, imagine them a week before your book starts and show us one of their conversations. Or write a scene that doesn’t exist within the current time frame. Or you could take a minor character and show a conversation they have with a completely random person (like a bank teller). This can reveal information that you might be able to incorporate into your WIP as well.