Writers in the science fiction and fantasy fields talk a lot about worldbuilding, mostly because it’s a necessity in their genre. Stories set in past or contemporary consensus reality don’t need it, or at any rate don’t need it in the same way — they may need to show the reader a new or unfamiliar part of the world, but the writer doesn’t have to make that part up from scratch.
Building a world from scratch is hard work. Most writers, being only human, tend to concentrate on the aspects of the world that are of the most interest to them, or of the most importance to the story. A writer of hard science fiction might not be able to rest until he or she has got the orbital mechanics of their fictional planet’s fictional solar system all worked out to five decimal places. A different writer might be content to leave the moon and sun and stars set on “default”, but will insist on figuring out all the finer details of the local banking system and exactly how letters of credit work in the absence of faster-than-light interstellar communication. And yet a third writer may not care very much about either moons or money, but will be as thoroughly conversant with their imagined society’s rules of etiquette as the local version of Miss Manners or Emily Post.
The trick — one of the tricks, anyhow; there’s lots of them — is to think about the day-to-day implications and consequences of the worldbuilding bits that you’re concentrating on. For an example of the kind of thing it pays to think about, the blog Hello, Tailor has a post on the way worldbuilding in film is implicit in — or fails at being implicit in — the costuming. To quote the author:
The visuals of movies like Equilibrium and Gattaca (and Aeon Flux, and Ultraviolet…) are, to me, the costuming equivalent of all those thousands of hard sci-fi novels that concentrate on the science fiction but forget to give the characters human personalities. Even in a world where everyone is genetically engineered to perfection (Gattaca) or everyone is drugged with emotional inhibitors (Equilibrium), it’s never really articulated why people look so similar. And if they were pressured to wear identical outfits every day, they wouldn’t be dressed to the same degree of neatness, a trait that varies enormously from person to person. Not that this really makes much difference to the overall quality of the film: it’s just something that bugs me, personally.
Because in the long run, everything in your fictional world is connected. The length of your planet’s days and seasons, and the rise and fall of the tides in its seas, will have an effect on how long or short the working day is, and how hard the seasons are, which will effect in turn the way the local economy is set up, and who is hardworking but poor and who is rich and idle and what the politics are that arise from that division, which will in turn influence the social customs and the unwritten rules of behavior that are an etiquette-writer’s stock in trade.
You can’t trace out all of the connections — you are, after all, only human, and this world you’re making is only words — but you can trace out the ones you’re interested in, or that influence your plot, and that will be enough to convince your reader (at least for the length of time it takes to read a story) that you’ve seen them all.