1) Clarity: Not only does empathy kill laughs, but so does ambiguity, perplexity, and all forms of confusion. To keep the laughs rolling, everything must be clear, starting in the subtext. If a character is up to no good, the audience or reader may not know exactly what that no good is, but it should be crystal that what he’s up to is no good.
Language, too. Piles of blurry, verbose dialogue suffocate laughter. If you wish to write comedy, go back and review the principles of style covered in Chapters Five, Six, and Seven. Their every point applies absolutely to comedy writing. Focus in particular on the fundamentals of economy and clarity. The best jokes always use the fewest and clearest possible words.
2) Exaggeration: Comic dialogue thrives in the gap between cause and effect. The two most common techniques of exaggeration either bloat a minor cause into a major overstatement—“You stole my mommy!”—or shrink a major cause into a minor understatement—“The Harry Potter Theme Park is a hit with both anglophiles and pedophiles.” Comic exaggerations come in a variety of modes: dialects, non sequiturs, malapropisms, impersonations, pretense, sarcasm—all the way down the line to babble and nonsense.
3) Timing: As I noted above, jokes pivot around a two-part design: setup and payoff, a.k.a. punch. The setup arouses aggressive, defensive, and/or sexual emotions in the reader/audience; the punch explodes that energy into laughter. The punch, therefore, must arrive at the exact moment the setup’s emotional charge peaks. Too soon and you get a weak laugh; too late and you get a groan. Moreover, nothing must follow the punch that would stifle the laughter.