It's been too long since I've added to my list of prompts, so here is one of my favorites.
This prompt will require you to have a play that you haven't read or seen performed before. There are hundreds of plays online for free, but here are a few if you need help finding one. A movie script is likely to have scenes that are too short and too much action and direction within the parenthetical text.
As with many exercises/prompts in writing drama, the key here is to pay attention to how to minimize telling and focus on showing. Fiction obviously employs more description than drama, but many writers use this description to try and dump huge, clunky chunks of exposition or try to tell the reader what to think about what's going on or another character. With only dialogue and sparse description to work with in drama, a writer is forced to find other ways to tell their story. Valuable lessons, even when taken back into prose.
Prep: Read the first scene of the play. Pay very close attention to how the writer shapes both the characters, the exposition, and the tension using only dialogue and a few stage directions. No matter how awesome, compelling, embroiling, and interesting scene 1 is, stop reading.
Prompt: Without reading past scene 1, write a scene two of the play. Continue to use the characterization you noticed in scene 1 and develop the plot and tension. Write at least three pages (or more if you wish).
Don't forget to have fun!