Stole this game off another site, which I recommend you take a look at to give you an idea of what it’s about.
Start off with four words and continue the story adding four words at a time.
When a story eventually peters out or gets way too surreal someone can just start another one.
[edit: Keepnig a sentence going is part of the game so don’t just cop out with a period if it’s possible to continue. ]
Once upon a time…