Amongst the thousands of ways of looking at world-building, here is one simple version:
The duty of the fantasy world-builder is to look at our world, and ask herself: Could I do that differently?
Any ordinary fantasy work you will see or read will not be like this. Most of the things you will find in them are basically just carbon-copy pastiches of real-world stuff and the fantasy canon. It will be a simple world with supernatural elements tacked on top, and there’s nothing wrong with that. Even if you follow the creed written above, there is no need to answer the question in it. You can do whatever you like. But it would be great if every world-builder and fantasist would at least ask themselves those questions: by not doing so, they are depriving themselves of the possibility of straying from the beaten path.
Some things I’ve attempted to deviate in Ysi are the books of the setting. In King of Nowhere, the Closer’s archives are filled with books, but they are unlike books we know in our world: neither scrolls, nor codexes. I thought about what kind of forms a book, a long stretch of text set in a compact format, could take. One of the variant results was that which ended up in the story: a book that is a hybrid between a scroll and a codex. It is like a scroll in that each page is attached to each other, and you could pull it out like a rope, but like a book in that there are individual pages which you can flip: the book is a long scroll that has been folded into a concertina shape, like a fold-up map, which can be read by flipping the edges. When you come to the end of one side, you can turn the whole thing over, and start reading the other side.
A lot of the time, visual artists are great at this kind of thing. They have the acumen to creating visuals that they can distance from reality, while an author, if he doesn’t rely on illustration, has really no way from keeping the reader’s imagination unaffected and unpolluted with images from their experience. If you write a fantasy, and talk about a character’s clothing, it will be very hard for a normal reader to not imagine a dress from our own medieval past or from other sources. This can be fought by introducing alien-ness into the world by the gallon: if the reader’s expectations about the world are consistently off, then they will stop reality contamination of their image of the work, and will pay more attention to the description of even mundane things. This is what I should have kept in mind while writing King of Nowhere, but I didn’t really succeed, I fear. Well, hopefully the rewrite will fix that!