Even if you are not much of a joke-teller in social situations, you can learn to write fresh gags for your speeches. Pick any topic and punch it into the Internet and you will get more starting points than you can imagine (“peanut jokes” gets nearly a million hits).
Gene Perret suggests that you take jokes from books and simply adapt them to your purposes. He also recommends these approaches:
Write down everything you can think of that is interesting about a topic — nothing has to be funny in and of itself, but look for the odd angles.
Pair items that are similar or dissimilar.
Exaggerate and take things to their logical extreme (“if Noah took every type of insect on board, then imagine what it must have been like …”).
State a truth in an unusual way — something on people's minds. As George Bernard Shaw said, “If I want to tell a joke, I tell the truth: there's nothing funnier.”
Attack authority or criticize someone who is supposed to be untouchable. Irreverence will likely provoke a laugh.
Tell a story that is supposed to be a personal experience, then stretch the truth. You localize it by knowing audience pet peeves and things they are proud of, which will make it even funnier to them. Have a few one-liners leading up to the main punch line.
If you really want to get serious about giving fun speeches, you could even benefit from studying the art of writing humor. How to Write Funny edited by John Kachuba is the best guide, 29 chapters from masters of comedy like Tom Bodett, Andrei Codrescu, Jennifer Crusie, and Lois-Ann Yamanaka. Among the ideas the masters suggest are to think of an incongruous situation and treat it straight, or to provide a formula with limitless variations (the books in Teddy Kennedy's library, top-10 lists, a 25-second version of War and Peace).
John Vorhaus, author of The Comic Toolbox, flips the usual advice about telling the humorous truth. He advises to tell a lie about an unfunny truth, through exaggeration: “This line is so long, it's going to be getting its own zip code.”
In Comedy Writing Secrets, Melvin Helitzer lists some formulas that can be used, including plays on words (takeoffs and cliché reformulations), malaprops (misused words), reverses (a switch of viewpoints at the end of the joke), and pairing of two logical, but unconventional ideas.
Types of humor discussed include irony (using words to mean the opposite of their normal meaning or a juxtaposition of contrasting elements), satire (“humor with a moral”), and parody (imitating a literary style, but it could also be as simple as making up a phony bestseller list).