I've run a lot of one shots at game conventions. D&D, Battletech/Mechwarrior, James Bond, Traveller, Conspiracy X What you need are: A compelling situation with a clearly defined goal, so that it feels complete in either success or failure by game end. The scenario should be evocative of the genre; If you are having a fantasy scenario there should be wizards and a keep and a small ruin or dungeon, with lots of setting flavor. If you are playing a wild west game, you'll need a small town, horses, some kind of conflict, cattle men vs sheep ranchers optional. Cyberpunk you'd need a bad guy corporation, lots of guns, cyberwear, and some kind of thing involving sneaking around hacking etc etc. All of the above to set the scenes as set dressing, but you want your adventure to feel original or at least not generally a copy of a movie or something that the players might have seen. A set of pre-generated characters, at least as many as max players you have set up for. A good mix of races, classes and skills unless your game is something like: "Warrior Monks of the fist of Shao-lin against the Dragon Ninja" via Legend of the five rings RPG or something. Don't have it be all battle but don't have it be all narration, either. Make sure you get right to the story: the character have worked together or are all friends, already on the road to wherever, boom something happens, they meet minions or servants of the enemy and are propelled into conflict. Then something else then something else. They are sort of learning what is happening but not enough to cut right to the climax of the adventure. They need tools or gear or skills or something that they have to earn. Then it gets tough: a tough combat, a glimpse of the main bad guy (you set up a bad guy as a specific challenge over time because fighting cold weather means "I put on a coat. Done." Finally, they muster their resources and fight the last fight or overcome that least challenge. By the skin of their teeth, they make it...or don't. But if they have played smart and worked and thought, and used everything they have, they make it, even if some of their characters died. Whether they do or not depends on the flavor you want. Nice to have: Extra pre-generated characters so that there is some skill overlap among them and lots of choices of who can play who. The characters and situations could over time form an adventuring group, if you decided to extend it or keep going. In my own history I used to run a Traveller one shot every year in Ohio at a game convention. Each year the scenario there built on what had happened in game that year prior, so that the whole thing was a linked story. I had two guys drive 100 miles to be at the con yearly, and along with the other games they played, year after year, they played my game, along with 4 others who just joined at random. It was really neat to have a few guys really rooting for the game, even if it ran once a year. Good luck.