1.) Start at the beginning. Decide what sort of beings or creative force made the universe in which your characters came to be. Play with ideas on how people might misconstrue it, what kinds of rules it sets up for the universe, and what kind of religions can evolve from a world made that way.

Consider the physics. What if some atmospheric or magical element makes light behave differently? If your world is smaller or larger than Earth, consider how that might affect gravity and, therefore, how it affects how people build, what sort of transportation they might invent, and what sort of bodies they might have. It could even be that something about your universe leads to a whole different kind of physics.


2.) Start with the religions. Come up with your cultures, sink into what sorts of religions make sense of each one, and see if you can come up with a creation myth that seems feasible. (Or seems completely unfeasible in an interesting and feasible way. Yes, I just said that.)

Think of the religions on this world---objectively, if you can---and consider alternate explanations for the ways they say the world came to be. Explanations that could be misconstrued into the holy documents we have now.

[What about atheists, Chy?]

Yes, that, too. If you have an entire world of atheists, however, that's going to cause a lot of challenges in and of itself. All cultures, throughout history, have a tendency to seek explanations for why unexplained things happen. And they love to tell stories. I'm not sure I can imagine a world where no one does that, but that just means it'd be very impressive if a writer could pull it off.

Then again, maybe they did have religion and something occurred to obliterate the religious faiths of an entire world. That's an interesting thing to ponder.


3.) Purposefully keep it fuzzy. We all argue about the creation of our universe, so it makes sense that a writer wouldn't know how the characters' world appeared. But in that case, you really need to know all the arguments, all the angles, to make that world seem real. This can actually be significantly more difficult to do (well) than coming up with a solid creation myth. This is making a body without a backbone. And a lot of people do that, and make the argument that even in the real world, no one knows the true creation myth---but the best writers know the approaches of the different religions of their world or worlds.


4.) Another "lack of solid creation myth" can come into play in the alternate universe---alternate dimensions, urban fantasy, steam punk, alternate history, and the like. Rather than a creation myth, one often only has to pinpoint where the created world differs from ours. And go from there.

Harry Turtledove imagined that the South won the American Civil War (with some sci-fi, time-traveling help). Emma Bull in War for Oaks imagined that fae creatures are real, and put them in an urban setting. Charlaine Harris not only imagined vampires are real, but let the humans of her world know they're real.

It is still a form of creation myth, because the south winning the civil war or vampires being known to be real are major events that create a new world. In these cases even more than the others, the creation myth is likely to be a major point of the plot, so it's especially important to have all the details hammered out.