In Once Upon a Chicken, players create a story that unfolds as the game progresses. Each round, the "prompt" consists of the story so far—i.e. all of the selections from the previous rounds. Each player writes a continuation of the story, and then votes for his or her favorite among the other entries. At the end of the game, you'll find that you've generated a complete story.
To begin the game, each player writes down the initial segment of a story. When everyone's written one, each player reads his or her entry aloud to the group. Then everyone secretly votes for one favorite. (You can't vote for your own.) When everyone's ready, reveal. The entry with the most votes becomes the beginning of the story for this game. If there's a tie, break the tie using some random method.
Each succeeding round follows the pattern of the setup round. Each player writes down a continuation of the current story. When everyone's written one, each player reads his or her entry aloud to the group. Then everyone secretly votes for one favorite. (You can't vote for your own.) When everyone's ready, reveal. The entry with the most votes becomes the next part of the story. If there's a tie, the player whose entry was chosen on the previous round gets to break the tie. You are allowed to choose your own entry in this case.
When the group is ready to end the story, declare the current round to be the final one. Everyone should then write an ending to the story. Vote on the entries as normal, thus ending the story and the game. If you'd like, choose one player to read the entire story aloud.