In the ongoing Dungeons And Dragons campaign I'm running for two friends, the main characters had reached a major milestone in their adventures. After seven game sessions, our dwarven protagonists had to start a long journey out into the world, which mean for the first time in seven sessions, they would be travelling outside the valley we had created for them. It was uncharted territory... literally, as neither me nor the players had defined anything beyond the setting we had roleplayed in for the past four months! The map was blank!
It was time for some more collaborative world-building, so the three of us got together between sessions for a couple hours and a couple coffees. My goal was the same as it was when we first put together the game: to make sure everyone participating in the game had a say in what the next portion of our game would be.
Traditionally, the GM would shoulder most of this responsibility, creating the world and NPCs and situations, and let the players discover and explore. But then you run the risk of disinterested players, or players going down unexpected paths, or putting in hours of prep-work that never gets used. We had a lot of success with how the initial setting had been put together, there was no reason it couldn't work again.
So, over coffee, we roughed out a new country that our dwarven adventurers would have to cross. As players, they would be spending multiple game sessions in this new foreign land, so it had be as fascinating as we could make it. I would be GMing the players through this new setting for multiple game sessions, so it had to be just as fascinating to me, but also ripe with potential obstacles, dangers, goals, and situations I could throw at them.
What sort of land is it? What sort of climate is it? What is the dominant race in this land? What is the culture like? Wo is in charge? How are they in charge? How is land and government and culture connected to our previously defined dwarven setting? Do they trade? Are they allies or enemies or neutral? What is the main advantage to living here? What is the main disadvantage? What are a couple interesting elements we can throw in to mix things up, regardless of logic or common sense? Now can we stirr those new, interesting elements in properly?
Eventually we had a clear picture of our new land, a desert country named Tuat, ruled over by Dragonborn and Lizardfolk. We had a two of three city names, places that naturally evolved out of our ideas, but ended up standing on their own as we added cool twists. We didn't have clear good guys and bad guys, but instead had great swaths of greys for our heroes to get entangled in. We decided it was going to have a major dwarven city to start with, just to give our protagonists (who have never left their valley before nor travelled any significant distance away from home) a safe harbour to start, but from then on it would be a strange and different place from what they were used to.
I stopped everyone from going into too much detail, however, as that would come out during gameplay. The idea is to have a broad concept we all agreed upon going into the games. During future sessions, I as the GM could then add colours and flavours and opportunities and obstacles without having to explain why they are significant or what they mean in context. Here is so-and-so, the lizardfolk dockworker; all three of us would know his place in the pecking order, his role in this culture, why lizardfolk were labourers and dragonfolk were not, etc. The background knowledge would already be there, agreed upon by all of us.
Though we had a location, we didn't yet have any sort of plot. Wouldn't be much worth to put together a great setting if the characters just hop on some horses and ride straight through it! So now that Tuat was of interest to the players, it was time to make them interesting to the characters. We wanted to have built-in reasons for our two dwarves to get involved in things, to stick their noses in where they might not belong.
I had each of the two players come up with an NPC that they knew would gain the interest of their character. Not anyone they knew, obviously, but someone that once they heard of them, they would be drawn to like a moth to a flame. Someone who had some special knowledge or knew their family or had a particularly inviting secret, whatever. These NPCs should line up nicely with the character's goals.
Then I had each of the two players come up with an NPC that the character wanted to avoid. I wasn't looking for cliche villians or psychopaths, but some interesting individuals that would be nothing but bad news for the character. Someone the characters would definitely not want to interact with, would want to avoid. A dragonborn who hated all dwarves, a manipulative merchant that would betray them if given the chance, etc.
Next I switched it around. I had Player-A consider Player-B's interesting good character and add a detrimental twist to it. So-and-so is really good and great, but... complete the sentence. They have information about your family's history, but has severe gambling debts. They can lead you to secret dwarven ruins, but are currently awaiting trail and possible execution. Take something that we know for sure these characters are going for, and then have the players add a meaty conflict in it.
Same with the "bad" NPCs. Each player considered the other player's NPC, the one they wanted to avoid, than gave them an element that their dwarves wanted or needed. The dragonborn that hated all dwarves, maybe he's the only one who knows the secret path through the canyon. That manipulative merchant, he's the one who is owed those afore-mentioned gambling debts.
We knew it was really coming together when we started tying characters together and placing them in appropriate locations. Some of the twists of the good characters and honeypots of the bad characters were interlinked. That NPC would go great in that city, and in fact adds a great element to that city. This person would hear about that our dwarves the second that NPC started dealing with them. Before long, you could see a dotted line connecting places and characters and situations, stretching from the starting port of Tuat right across to the far side.
After a single night, we went from having literally no where for our game to go to three full pages of notes and an entirely new game setting and he clear seeds of several great plots. Like a good movie trailer, it might give away most of the general plot, but it leaves so much room to play with that you can't help but participate. As a GM I don't have to worry about whether what I present in an upcoming session is going to capture the players imagination. That's now guaranteed. Now all I have to do is surprise them with the details :)