There are three things which are real—God, human folly, and laughter. The first two are beyond our comprehension, so we must do what we can with the third.
—John Fitzgerald Kennedy
I remember the first joke I ever heard. My father told it frequently, whenever my sister and I got particularly annoying:
Three elderly women were sitting on the beach in Miami. Two were talking about their children. The first one said, "Ah, my son is a lawyer, makes $250,000 a year, drives a Jaguar, and sends me down here to enjoy the sun for one month every year, and he and my two grandchildren call me up every other week to see how I'm doing." The second woman said, "That's nice, but my son is a plastic surgeon, and makes $500,000 a year. He and his wife have twin Mercedes Benzes, and he sends me here for three months every year and my adoring grandchildren call me every week to see how I'm doing." They turned expectantly to the third woman, who said, "I'm sorry to disappoint you, but I have no children." In unison, the other women said, "What on Earth do you do for aggravation?"
This joke, which sticks so relentlessly in my mind, seems to me a model of technique. A joke is a short short story, one carefully propelled by skillful clues and deliberate miscues. Most jokes are designed to reach a sudden, surprising climax, one that triggers an explosion of laughter.
Why can humor be such an effective device for a public speaker? The most obvious reason is that a good story entertains your listeners. It makes them feel good, makes them more responsive to what you have to say, and convinces them that you're a "regular" person with a good sense of humor. Used with restraint, humor can also make your ideas more memorable, clarify your points, and persuade your listeners.
Restraint is the key word. Go for smiles and chuckles, not belly laughs. You want people to pay attention, not to roll in the aisles (unless, of course, you're a humorist and your main purpose is to entertain). The goal of a powerful speaker's humor is to keep the audience involved.