The Three Steps: Know
Know Your Story
Eventually, you become an expert on every part of your story. You know who everyone is and what they all do and why, and when and where each thing happens. This is the part where you can really work on making the story work.
Foreshadowing
Once you figure out what is going to happen in your story, it's polite to go back and add in little hints and clues and promises to the earlier parts of your story. It's a tricky thing to get just right, but your plot need to be just surprising enough, without being so surprising that your audience gets confused.
Themes and Arcs
Eventually, you figure out what your story is about. Not just what happens, but what it's actually about, right down in its core. That's when you can go back and weave that core idea through the whole story, and make everything subtly point at it. Or you figure out who your characters are changing into as they go through the story, and make that growth happen slowly across the whole arc of the story.
Worldbuilding
Maybe your story starts out without much detail. That's fine. But as you write down the story maybe you start to find out more and more little things about the world of that story. Now you can go back and add these details in more places, filling in the bland parts with rich details that make the world feel alive.