Make sure the epilogue is not used simply to retell the existing story.
Encourage students to include specific examples of what a character did next in the epilogue, not generalities.
Ask students to think about how a character was changed by events following the close of the story and describe how those events manifest in the person who now appears in the epilogue. Hold them responsible to clarify the motivation for a character's actions and the consequences of same.
Allow interesting twists of plot in the epilogue but stress that events should follow the arc of character development established in the main narrative. Draw out a student for more explanation if the shy, school poetry contest winner of the last chapter becomes a world-renowned trapeze artist in the epilogue. Point out the necessity to allow characters to evolve and triumph while keeping the story line plausible.
Use the epilogue to introduce students to the skills of writing personal narrative. Encourage the inclusion of dialogue, descriptive prose and plot dynamics to complement those same elements just encountered in the main story.