Creating a setting for a tabletop roleplaying game is a lot of work. Regardless of whether it is supposed to be the backdrop for an entire campaign or a temporary location your players find themselves, it takes a lot of work to get it ready. I have had a lot of experience creating worlds, given that it was always my favorite part of writing stories and running D&D games, and I’ve learned a lot of lessons about how to do it effectively and quickly. Not every setting can be created quickly, of course, some things just take time to work out, but I have a few tips and principles I stick to that help me create something I can use without making it so rigid that there’s no room to improvise and adapt as your players (or characters, for written stories) explore.
Core to this practice is the difference between knowing and understanding (in this context). If you know a world you’ve created, you can spout an endless list of facts and share juicy tidbits of places you’ve already written into existence. If you understand it, you can provide the answers to any questions someone might ask you. Ideally, you would strive for both if you’re writing a story, finding your comfort zone between the two so you can be prepared for anything that comes up in a story without spending so much time on world creation that you never get started recording the story. In a tabletop game, the balance is different and understanding frequently serves an open and engaged GM better than knowing. After all, if you already know where in the world something like Nutella exists, then you might spoil your players’ attempts to have fun by telling them that cacao grows in a different hemisphere and the lack of internation shipping means it hasn’t made its way to the location your game is happening so they wouldn’t even know what chocolate is to ask for it.
The first thing I make sure I understand is what state the world is in and why it got to be in that state. The answer can be as simple as “slowly decaying as it is twisted into an extra layer of hell because the good guys lost a long time ago” or as complex as “slowly twisting into an unrecognizable form to the eyes of the once inhabitants as it undergoes an upsettingly swift ecological change from a habitat that supports mortal lifeforms to a habitat that supports infernal or demonic life forms, complete with brand new forms of life and many, many old forms of life that either proved hardy enough to survive the change or adaptable enough to thrive because someone made a deal with an ecoterrorist that resulted in a series of regime changes that left the world government in poor shape to respond to the emerging threat that was the continent a bunch of people lived on suddenly waking up and threatening to eat the entire world.” I’d done both and both have created incredibly similar games that were both very fun to play but emphasized very different aspects of the game that would happen in them. The simple description’s game was about reclaiming what was lost and succeeding where one’s forebearers had failed and the complex description’s game was about learning to abandon old prejudices, adapting to a changing world, and finding ways to make a world that is suitable for everyone who wished to live in it.
You can dive deeper into all that if you wish, filling out as much detail as you like, but if you understand the basics already, you can move on to the next step: understanding the grand scale political structure of the world. Who or what has power, who wants power, who has some power, who has no power, who is using power in a generally desirable manner, and finally who is using power in a generally undesirable manner. The word “desirable” is key in those last two because it tells you what the general feeling is about those who wield power. Even in an evil society, full of people who embrace evil and selfishness, those who wield power in those ways will largely be as hated as they would be if they were a tyrant ruling over a more altruistic society. The motivations for why people dislike or wish to replace those in power will change drastically from one society to the other, but the person or group wielding power will be disliked either way. You could figure out why, EXACTLY, everyone in a city dislikes the king, but it’s usually better to understand why people would dislike the king and know why a few, specific, and important people would dislike the king. Plus, chances are good that those people represent large swathes of the population so you’ve basically figured it out for all those people as well if you understand why that person’s views might appeal to people other than them.
Once you’ve figured out the political and power situation to the point of comfortable understanding and selective knowing, turn your attention to the people who aren’t included in those bubbles. Why weren’t they included? What about them sets them apart from the people who are covered in your earlier bubbles? The line between understanding and knowing starts to lean more towards knowing at this point, since you need to figure out what sets this population apart, and that helps since this is usually the scale individual players (or characters in stories) will start to engage with the world at large. You’ll need to figure this out based on your own comfort levels (for example, I always need the names of people and places prepared ahead of time, or else I wind up giving things absurd names that reflect what they are and giving people masculine-leaning names of five letters or less), and there’s no replacement for experience when it comes to that.
When it comes to mechanics and figuring out why systems work the way they do, it’s always good to come up with guiding principles, basic rules, and then to record every time you use those two things to create a more complex rule. For example, if you’re running a game for a group of people that find themselves in an infernal wasteland that is slowly growing, a basic rule is that “everything growing here is immune to fire” and a guiding principle would be “the players need to want to explore this place enough to make it worth the hassle of surviving this environment.” If you know those two things, you can easily adapt them to create complex rules like “wood from this area won’t burn, but armor made from the tougher trees here will partially protect the bearer from fire damage and a spellcaster using reagents from this place would get a bonus to the damage their fire spells deal or could turn a spell of a different element into a fire spell.” Using a set of basic rules and guiding principles, you’ll have enough information to make a decision at a moment’s notice that will reward a player’s ingenuity or encourage players to spend more time investigating this neat environment you’ve created.
There are a thousand other small thoughts and ideas that I could share to help you create a world, but most of them boil down to what I’ve written here. There are always exceptions to any rule and the main point of learning the rules to any creative endeavor are so you know when it’s appropriate to break them, so take all of this with a grain of salt. If nothing else, I hope it helps you think about what you’re creating or sparks an idea that makes your creativity easier.