Guide of Modos
I have no idea how the Cast of Thrones game finished, but it seems that everyone had a good time at it! It seemed to use the standard formula: hey you, do this, and report back to me. Which is straight-forward, but it doesn't provide for much cohesion or originality. Are these necessary in a one-shot game?
I've been using pre-generated characters for one-shot games, which gives me the chance to add some character goals and relationships. I can run just about any type of quest I want with those in place, at the cost of player dissatisfaction with character customization. I also like to check in on each player, even (especially) interrupting jokesters who aren't actively role-playing, to make sure everyone is feeling included.
What types of plot do you use?
Are there character requirements?
How do you keep the game on track?