One obvious question in terms of your fantasy/sci fi world is what you need for your story. Just a simple nuts and bolts question of what your story needs to run. If you have, for example, a very classic fantasy arrangement of a barbarian in civilised lands, undertaking a quest for royalty that brings him or her into conflict with a wizard after a long journey and many fights against non-human monsters, then you know a few things about your fantasy world from the start.
You know that it has a division (false or otherwise) between civilised and barbarous lands. You know that it has at least one kingdom or empire, which might be small, but at least has a royal ruler (and thus presumably a social structure that supports that). You know that you have a world with either magic or the appearance of it, and it is a world with monsters in it.
These are very simple observations, but I find one of the things about world building is that it’s possible to build from simple observations to something more interesting and useful. Whereas if you build from complex thinking about your world to your story, it doesn’t always work. If you know what elements are in your story, then you know the bare minimum of things and relationships that have to be in your world, whereas I live in dread of creating a world that has no room for the story I have in mind.
More than that, you can create a lot from these simple piece by piece observations simply by asking yourself where each element comes from and where it fits in. Rather than stifling creativity, it should spark it, by giving you a whole list of things where you have the space to build detail. It also helps if you’re constantly asking two questions in conjunction.
The first is ‘so, what’s an interesting way of approaching that element?’ The idea of these story components leaves you usually with a list of clichés mixed in with some more imaginative things from your original inspiration. Because it’s just a list, rather than a worked out world at this stage, you have the freedom to brainstorm more imaginative options. For example, if we take the royalty before, we might go with the stock all powerful emperor or pseudo Egyptian/Persian god-king. Or we might go with the nominal king of a country who is in fact in charge of very little (a la Louis VI of France), or the chief Elvis impersonator on a planet full of them, or a monarch in hiding after a revolution, or a constitutional monarch so tied down by convention that an outsider is the only way to get anything done.
Which brings us to the second question we have to ask, which is ‘yes, but how does it work?’ For me, a lot of fantasy is about the interaction of the imagination and the consequences of that imagination. Thinking about why things are as they are, how they could possibly work, or simply what comes out of them logically is a great way to get more of your world on a plate. For example, a world where everything is made of cheese might give us as an obvious threat a horde of super intelligent mice.
I put that one in to make the point that I’m not asking everyone to switch over to hard sci-fi levels of rigour here. It’s about one part of the imagination sparking another, to whatever level of rigour, common sense and logic you feel is appropriate (in comic fantasy, there will generally be more logic than common sense, so that if there are dungeons full of traps and treasure, then of course there will be strange little companies that build the things, industry awards for doing so, and magazines entitled ‘What Dungeon’)
It’s just… well, if we take our monarch without much power or land above, then we have to ask the question of how he or she is still a monarch, and the answers to that tell us more about the world. And when we pick at how that fits together, that tells us more still. So maybe we have a situation where our ruler rules a very small area that is effectively shut off from the world, and his near godlike status is down to his own delusions, while the ‘barbarians’ outside the gates aren’t all that barbarous, but don’t invade because he is nominally their ruler still, and if you go around overthrowing your ruler, then maybe people will start wondering why they can’t overthrow you. Suddenly, just from taking an idea and asking how it could work, we have the beginnings of somewhere that feels a bit more real. Beginnings that we can expand on by reverting to our first question, or by bringing in some of the other ideas we generated. Combining ideas is always fun.
So give it a try. For me, the advantage of this approach is that it puts you somewhere between the plotter and the pantser when it comes to world building. You’re sure that your world is connected to your story, but you also have the time to come up with novel elements for it that you might not have put in on the fly.