World building is the foundation of epic fantasy. Since I mostly deal in epic fantasy and sci-fi worlds and since I assume some of you care about my writing, I thought I'd share a bit of how I go about my world development. Now often times I don't plan things out or write it all down in a wiki or bible, so this might come off as a bit abstract, but since that's part of how I do it, that's how this is going to be written out.
Contrary to how some people might, I don't start out building a society or culture or kingdoms when developing a new story. I start with the main character. Generally I will start by writing out a description of what they look like. Then I'll do a basic interview. I'll want to know some of their likes, dislikes, pet peeves, something about their living conditions. Now this doesn't, and shouldn't be very in depth. I don't know what all of my character's favorite breakfasts are, or their favorite color. I also do this very quick. If I do think "What is their favorite color?" and nothing comes to me in about ten seconds then I will assume it is unimportant to the story and not worth dwelling on. The important part here is to not get hung up on tiny details, but to get a general idea. Having a few unknown hooks for later is nice. For example you might notice a scar on their arm, or that they are wearing a necklace with a pendent. You don't have to immediately know the story of the scar or the meaning of the pendent, just that it's there to come back to later.
I know, you're thinking "Damn it Wesley this is suppose to be about world building, not character building." You're right, this is about world building, and the characters define the world. We also want to build a world where our main characters fit. (Unless that's the premise of your story but that's for another time). I start with a character and then I want to know about their world. So I think about what I've learned,d their likes dislikes, attitudes and that's where I start mapping out what kind of things would lead to these traits. If they love grapes, why do they love them? Where do grapes come from in the world, are they rare, common, a treat? Do they get into fights easily? Why, are they trying to prove something to themselves, do they just not like bullies? Are they a bully themselves?
Also you build this character you have to start filling in details of the society, what does that society value. Is your character rebelling against those values, trying to uphold them? With this frame work you can transition into building the starting town/country/kingdom/empire/confederation/whatever. The first location should have lots of details. It is the place your MC is likely the most familiar with, or even if they are new they are going to be experiencing a lot of exciting new things for the first time. Giving your starting point everything from government organization, common foods, dresses, entertainment preferences gives your world life.
But you don't want to just describe a fantasy town and then have nothing off to the sides. Unless part of your plot is that going 20 miles from down is the end of the earth and you fall off, you want to make sure your readers know their is a fully formed and functional world.
This doesn't mean you spend 4 pages describing the neighboring kingdom. you'll want to give neighboring locations priorities. If it is close to your MC's starting point and somewhere they might go or interact with the inhabitants a lot, more detail is better, but the further out you go the less details you need. For example if there are countries across a sea that your MC knows about but isn't likely to travel to themselves, you don't need a lot of facts about them. But these are good for throwing in something that might be exotic to the characters. strange magic, fruit, music, a strange visitor. All of these can be from a place far way that we don't know much about. We don't need to know much about it because it might not be important to the story. A detail here and there is enough to keep the reader guessing without giving so much away that it makes it boring or bogs down your story.
If you do end up writing out a lot about a place you end up not using, that's okay too. Knowing when a place and it's features aren't going to be important to the story is part of world building in a novel. Include the bits of the world the reader needs to know at the appropriate time in the text.
Even if you do end up visiting a place far away in the story without a lot of details that's okay! You can provide a few details relevant and leave the rest a bit of a mystery. Leaving hints that there's more going on in a land then your MC is exposed too but can't investigate leaves room to grow in a place later on.
The most important thing is to remember that you want to make sure your world seems viable without bogging down the story. Tell your story first, then add in little details later to breath life into the world, I've found this easier than trying to create several different nations that feel unique enough to matter but aren't really relevant.