World building is the process of creating a world that your characters inhabit in your book. I'm in the middle of writing coaching two authors working on their books, one mystery and one vampire novel, and world building is center stage. The first book features a protagonist figuring out what's causing an outbreak in his town. He's got a clock he's racing against and people he cares about on the line. This book takes place in a world that is close to our world. The second book is a vampire novel that features the protagonist on the run from an antagonist as they navigate a centuries old grudge. This book takes place in a world that the author has created.
I'm focused on making the authors define the world they've created. Here are the three things I've been asking as I help them revise:
Q1: What needs to be defined?
A: For the vampire novel, the reader needs to know how your vampires are supposed to act. Are they 30 Days of Night scary? Are they Twilight sparkly? Do they eat food, not go out in sunlight, have superhuman strength, murderous tempers, etc? Your reader needs to know this so they understand how your vampires operate in the story. This applies to other novels that rely heavily on creating a new world. How does the world operate. You should know the bulk of this as you write.
Q2: What conforms to our reality?
A: For the mystery, since it takes place in our reality. That means gravity, speed laws, and chemical reactions are going to conform to real life. But the important thing to take away is that the reader may not know the information you're using to shape your world. Do they need a crash course in marine biology, mortuary practices, or how to hack a phone? Sometimes you don't need to change our world for your reader, but define the pieces of it that the reader needs to know to understand the book.
Q3: How soon do you define the world?
A: This varies for each book. For the vampire novel, I'd say from the start because the reader wants to know how the vampires operate. What does the reader need to know about their strengths and weaknesses? For the mystery, it depends on what the reader needs to know to believe that the main character is in control as they investigate the story.