Iterative World Building

 As a science fiction writer, especially one interested in relatively hard far future sci-fi, I spend a lot of time world building and thinking about world building.

When it comes to creating your own worlds, solar systems, or even universal empires, imagination is the limit. But that doesn't mean you can do whatever you want. Regardless of whether your story is high fantasy, hard sci-fi or even super-soft, let physics be damned, sci-fi, all world-building has to follow a one important rule.

Be consistent. Your rules, whichever ones you come up with, must be consistently applied throughout the world. If they are not, there must be a good reason. A very good reason that is, itself, consistent with the rules.

This is the crucial, guiding principle in world-building and is the difference between a believable world (even a high fantasy one) and a laughable world.

The extreme cases are possibly easier than those closer to home because it's more obvious that you're developing an entirely new world.For mundane sci-fi or urban fantasy, however, an author must be careful to clearly delineate the boundaries of where 'our world' ends and the story world begins. This includes understanding the consequences as they would play out in the world. This must be obvious to the author before they write, or they will never be able to convince their readers.

So, you have a great world-building idea, how do you make it believable?

Well, it's important to realize that the world doesn't make your story, you still need great characters and compelling plots for that. But the world will guide your story, lend its character and features to your story. If it does not, there is no use setting your story in this world. The world must be a reflection of the story you want to tell, and vice versa. Having said that, on to more world-building.

The first thing you must realize is that your idea, in it's crude form, has a 99.99% chance of having been done before. What you're looking for is a way to make it uniquely yours. For that you need to explore hidden areas, find consequences that haven't been thought of, or at least tried in this context, before.

For example, a region of floating stones. It's been done many times (Dungeons and Dragons, and Avatar come quickly to mind), yet the idea still has an interesting allure. The first thing to ask yourself is why are they there? After all, they're something so foreign to our experience. You'll start with the basics:

Fantasy -- built by ancient wizards / gods
Sci-fi -- built by ancient race / electromagnetic anomaly combined with rare alloys

The important thing to do is challenge the tropes. e.g. Instead, perhaps they are exceedingly bouyant structures and there is high density at that area, or they could be camoflaged ships, or illusions. Maybe they are actually suspended in a network of fine cables or set on invisible columns. Whatever you decide, the important thing is not to settle for the easy answer.

After you decide on the general, move to the specific. What type of people / culture lives in, developed around these rocks. Do they live amidst the rocks, above, below them? In one massive city or smaller tribes. Perhaps each rock is a colony. Were these the original builders/occupiers or did they only find the rocks.

From here you move into ideas about the people's appearance and social development and even 'secondary effects'--those less foreseen consequences of human nature in such an environment: how do they communicate? what is they driving motivation (sex, food, water, territory, raising young)?

The important things is, at each stage, to keep asking yourself any and all questions you can think of. And when you can't think of any more, ask your friends. While most of the information will not make it into the story, the more you as the author knows, the more believable the story will be.

At this stage you may turn to character and, most likely, certain ideas will come to you straight away. Resist them. The first ideas will, most likely, be bog-standard tropes. Dig deeper, ask yourself more questions on the characters, the community and what would make an intersting story in this world. Once you have an idea, ask some more questions. You will eventually hit upon that 'aha' idea that will really light your fire. Build on that. But don't stop asking questions.

In reality, the world building and story building process generally work in tandem since experienced authors have some idea of the story they want to tell before hand and are buiding a world in which to highlight issues and ideas they have. However, it's important to realize that in all other facets, the process remains essentially as described. The key thing is to never be satisfied with your first answer, always ask yourself what else might be possible.