To give a quick idea of the difference for me between a long campaign and a one-shot. My long campaigns run a little over a year, and my One-shots run about 4-6 hours.
When plotting out long term campaigns, before we start the campaign, I tend to have a beginning and an end in mind with a few things that I know I want my players to experience. For example, in my world of Darkness Campaign I knew I wanted them to go into the spirit world and interact with fairy tales. I also wanted them to meet a character named John Smith who would always be on the cusp between good and evil. Generally, the themes and vague ideas are hashed out about the plot, but I like creating “sandbox” worlds where characters can go anywhere they want. After I give my players some ideas about the world, I ask for backstories, and try to incorporate the backstories into the plot as well.
With a skeleton of an idea, I then start the run. From there, I plan weekly based on what I feel my players are wanting, and making sure there is a balance between combat, skill challenges, and character development. One of the big things I like to do, is make sure that my worlds are safe places to explore. I want my players to have creative ways to find information or to go anywhere they want, though I always try to give them hints to lead them to places that will include progress in their quest.
I’m never quite sure what my players will do, so I never have a “right way” in mind for them to do things. I find this is very important to long term campaigns, letting the characters experience the world while giving them hints to the plot at hand seems to work well. Each week I study new things that I might incorporate into the plot.
Long Campaigns are great for letting me work out long complicated stories. They give me time to slowly reveal clues, and in turn watch as characters change how they think about something or someone. I love creating a world and watching other people add to it as they make their way in it. Work on these games end up in the hundreds if not close to thousands of hours a year, but are amazingly satisfying when completed.
In some ways one-shots take more prep per hour played. Mostly because in order to keep the players on track I have to map out each major plot point and battle. There’s no time to reflect between sessions on if things are moving too slowly or too quickly. Instead, of having a beginning and end, I have all the major story points.
Generally, I find a good 4-5 hour run has 2 1/2-4 battles. The first one usually being a warm up to help the characters figure out how to work together. I also tend to have some event that throws the characters together rather than letting it happen naturally like I do with Longer Campaigns. For example, in my next one-shot they all take refuge at the same castle after a flash flood. I also tend to push a little bit harder to keep characters on track so I need to know exactly what that track looks like. That being said, I usually have one or two ideas of how they might solve a problem and find my players solve it in a very different way.
One of the things, I love about one-shots is it allows me to experiment with various themes and ideas without being too heavily invested. I can have the survival horror story without a year of zombies.
A few things I always do for both, is think what story I want to get across. Is it going to be a little goofy, scary, sad? In the end, how do I want my players to feel and experience. Overall, they’re both work, but I can’t imagine not running games.