I talk a lot about elements of worldbuilding, but rarely about what it is. To me, it all boils down to this:
Worldbuilding is the art of creating a fictional world that a reader can accept as real.
That’s the core of what I look for in worldbuilding. Can I imagine that this world I’m reading about exists beyond the borders of the page. Are there hints of faraway places, other cultures, a history, a society. The best worldbuilding inspires fans to create maps and artwork, to speculate on “what if” scenarios and wonder how past heroes would fare in the “modern age.” The worst worldbuilding is like a high school play, with a cardboard backdrop that everyone knows is fake. If the actions of the characters are interesting enough, you can overlook it, but it’s better if the reader isn’t asked to try.
How much world to build
The answer to this is: as much as you need, then as much more as you like.
There is no limit to how detailed and complex you make your world. You are bound only by the amount of time you’re willing to invest and the challenges of keeping all the pieces working believably together. If you are writing professionally, you will find that beyond a certain point, worldbuilding becomes a time sink, keeping you from putting your stories into words. If you are writing as a hobby, feel free to go into as much detail as you like: render your cities in 3D, construct working languages, write history books. There is a certain pleasure in creation that is undeniable, and if that’s what you want to spend your time on, by all means do so.
How much world to show
This is where we get into the harder questions. You need to show your reader what is relevant to the story. No more. No less. Maybe your hero’s hometown sits on a river that was diverted from its course 1000 years ago by a great wizard’s battle. Is that interesting? Sure. Should you include it in your story? No, not unless that fact comes to bear on the story.
Focus on writing the happenings of your story. Use your worldbuilding facts as references for you, then show the reader the result. Don’t lecture. If anything sounds like it came from a 7th grade social studies report, edit it out.
Jenna removed her prayer beads and dipped them in the shrine’s basin, letting the blessed waters remove the taint of her recent trials.
Jenna removed her necklace and restored its powers. Priestesses of Shie were able to use the holy waters found in the shrines to counteract the evils they battled. The ritual had been handed down since the time of the Budding Empire, and every acolyte learned the chant. There was not a city in the empire that was without such a shrine.
If you find yourself rambling, or talking about things that won’t come up as important to your story, consider trimming them. Remember, you’re telling a story, not telling a world.
What not to build yourself
This is a personal decision for every writer of speculative fiction. How much is the right amount of Earth to leave in your world. If you haven’t read it yet, check out my article on “default” assumptions of a fantasy world. Anything you don’t specify as unique to your world, readers will fill in from their own imaginations.
Does your world have real-world animals, new but otherwise plausible creatures, or fantastical beasts? How many moons are in the sky? Are humans the only sentient race? You can change anything and everything. Just beware:
Every departure from your reader’s assumptions will require explanation, or the reader will become confused.
It’s fine to confuse your reader a little, but there is an unspoken agreement that all will be explained in time. If you drag a reader around for hundreds of pages in a befuddled fog, then just leave them there, you’re going to end up with unhappy readers (and probably some bad reviews). If you don’t like explaining (or find you can’t do it without info dumps), then cut back on the number of changes from “fantasy standard.”