When I prepare one-shots, I do it with the intention of running it more than once. Somewhere, some day, I may be in another group and need a fill-in between regular campaign sessions. I may want or need something to run at a convention or game day. The only thing that makes it a “one-shot” is that it’s a single adventure not tied to a regular campaign, meant to be run in one sitting of 2 to 4 hours.
Because this may be the only time I ever sit down with a particular group of players, I want to make a good impression. Because I don’t know the players, I can’t anticipate their needs and their styles of play. That’s why I tend to do a lot more research for a one-shot than I do for an ongoing campaign. It’s the difference between a low-budget television series, with a new episode every week, and a big-budget movie where you only get one change to pull out all the shots and do something really special.
A lot of these things are done to save time, so you and players can focus on the adventure and not be answering esoteric questions and looking up rules.
If there are any encounters that will require special rules, make a cheat sheet to hand to the players. Wait until the moment, or shortly before, so they’re not fiddling with papers when they should be paying attention to the game. If a per-generated character has a special ability, make a handout for that player explaining how it works. It saves time looking up rules later.
Maps and Photos
Even if you’re not engaged in a traditional dungeon crawl or playing a game that uses miniatures, maps help set the scene. In modern-era games, I will print Google maps of a town, or an area the players will be in. Questions from players then center on specifics — “if the window regular glass, or safety glass” rather than “is there a window”. Photos also help set the scene and answer questions. For modern games in real-life locations, I find pics of buildings, interiors, anything that’s relevant. If players will search for clues, a pic of a room let’s them know there’s a sofa to look under of a desk with drawers to rifle through. Even in fantasy games, pictures of castles, ruins, even forests and terrain helps. When you get to fights, it helps them envision tactics better than a flat map.
I also find pictures of people to represent important non-player characters. I write the character’s name on the picture, and put it on the table. It helps players remember who they’re talking to, and they often make notes on the picture to help remember the context of the character and why they’re important.
Photos of props help too. Guns, swords, cars, anything that’s a relevant object. Again, it helps them remember that the object is there and is important, and they can take notes on it.
News, Weather, Sports
I’m currently working on a Delta Green one-shot, based on a published adventure. It’s got specific dates and real-world locations in it. I thought it would be fun to see what else was going on in the news that day, so as the players drive to the scene from the airport I can do some banter from the car radio. I found out that there was a violent hail storm that day, and yucky drizzling rain for the whole week after. Perfect! What a great detail. The hail caused a ball game to be delayed. There was also a UFO sighting, carried by all the major local news stations, and I found a clip on YouTube! The UFO has nothing to do with the plot, but the players don’t know that, it helps set the mood, and now I have a red herring I can work in.
Even if you’re using a fantasy setting, these kinds of details can help get players deeper into the game. It adds some depth and realism, and sometimes it can help them forgive some of the more fantastic elements of a plot, or overlook huge gaping plot holes that may exist. “It was the time of th coronation of King Ludwig” might have no bearing on the adventure, but it does a little bit of shorthand worldbuilding that makes it stand out from other generic adventures. Knowing that the players spend the whole game inside a dungeon doesn’t mean that it’s springtime and sunny outside doesn’t matter; it provides contrast, and impacts how they feel about being in the damp and darkness.
Research in Ongoing Campaigns
I do these things in ongoing games too, of course, but not in as much detail. Who has the time? I restrict research to photos and maps of recurring locations and supporting characters we’ll see a lot of. In a one-shot, I may have a photo of the innkeeper you’ll spend all of 5 minutes talking to; in a regular game, no way.
The difference in preparation, I think, is between story and character. In a one-shot, there’s not a lot of character development for player characters, at least no more than you need for the story itself. For that reason, more attention to little details matters. The story is the star, so a focus whatever makes it pop. In an ongoing campaign, I want to focus on the characters’ reaction to the events, the personal subplots and goals. I also put some of the onus for that research on them; tell me about your character’s house, their relatives and mentors and enemies. You need a lot less showiness, and more emotional texture. It’s a different balance, and requires a different sort of preparation.