Think of at least two of the characters that may appear in the work and imagine them trapped in a peculiar situation together; perhaps they're stuck in an elevator. Consider their speech patters, mannerisms and quirks and ask yourself what is funny about these characters and what comedic or serious conflicts these two may have together. What situations might they find themselves in outside of the elevator?
Outline the plot of the story, breaking down the plot into scenes, considering what is poignantly dramatic or profoundly comedic about each scene being examined. Which scenes call for laughs and what scenes call for dramatic revelation? Where in the scene is the space for jokes and where is the space for tension?
Write out an entire rough draft version of a scene, using your outline and previous writing exercises as guides to how the characters interact.
Review the scene aloud with trusted editors or friends to gauge what works in the scene and what doesn't. Consider what jokes fell flat or what plot points may confuse your audience and then adjust your work accordingly.
Continue writing scenes until you have a rough draft manuscript. Repeat the audience-gauging and the revising process until you have a dramatic-comedic manuscript that you are satisfied with.