Choose your starting and ending points for the narrative. Your epilogue will be divided into periods. Each Period is a large chunk of time measured in years or even decades.
Each period should have an evocative description and a Tone—light or dark.
Next, take a step back and create the Palette for your game. This is a list of things the players agree to reserve the right to include or prohibit. This will be an aid to ensure that everyone is in agreement about what belongs (and doesn't belong) in the epilogue.
Since Epilogue is played after the conclusion of a campaign, the items in the palette will usually be focused on things that the characters can or can not do after the campaign. (This is different from a standard Microscope game, where the palette is more far-reaching.)
NOTE: Creating this palette can be challenging since the scope is small. If the players only come up with a couple, that is fine!
For the first round the group should create things that happen in the world and not to the player's characters. This will give things for the characters to react to.
Choose one player to go first. That player creates either a Period or an Event. (No Scenes at this point in the game.) Play continues until everyone has had two turns to add things.