I played several games of Odyssey (very neat game about how the trip can change the nature of your character).
There is a mechanic about making list of scenes to play, made by each player, that become available randomly at each turn.
It is a lot of fun to choose between a restrective set of premade scene (changing at each turn) to launch your scene. In fact, players launch scene a lot more easely this way.
I think you can directly use this in your game (not tested this yet).
1. Choose the theme of the episode.
2. Give 6 blank index cards to each player (GM included).
3. Have every one write a very short scene idea on every card : it should just be a very short sentence that is generic enough so that anyone could use it in his own way and intergate it easely in the story (examples coming from Odyssey character sheet : "Velociraptor attacks", "love blooms").
Now, before every scene.
4. Shuffle the cards
5. Draw as many cards as there are players (if you are 4 players GM included, draw 4 cards)
6. The player may or may not use a card to launch a scene. If he uses a card, then discard it.
7. Put the remaining cards back in the deck.
At any moment in the game :
8. A player write a new card and put it in the deck.