Now and then, friends and family ask me for jokes to for best man's speeches. I wish they wouldn't. If they wanted a half-hour story with a sub-plot and a set-piece ending, I could help. But stand-alone wedding jokes? Nope. Can't help. I can't even suggest they jokes from the great joke writers of our day (I'm thinking Milton Jones or Steven Wright) because I know they won't credit them and that would be annoying.
So in this situation all I simply give it two pieces of advice that I know they won't appreciate and will probably ignore, but know they'd thank me if they took it. And this advice is not about the jokes specifically but the audience and their expectations. Expectations are everything. This theme crops up many times in Jonathan Lynn's excellent book about the rules of comedy (that you should definitely read) so it must be important.
The first thing is to point out that the audience is mostly made up of the bride and groom's family. The father of the bride speaks first. At least half the room know him. Then groom stands up. Half the room know him too. And then the best man stands up. Most people in the room do not know him. What's more, they are worried about the speech and the possibility of rudeness and offence (always on behalf of others, you understand). Know your audience. What are the expecting? Meet their expectations so they don't worry, but delight them so they enjoy it. And they'll enjoy it if you keep it clean. Seriously. It's not prudishness. It's just basic audience dynamics.
The second tip is related to the first. If you want to delight your audience, finish early. End before the audience want you to. (The phrase is "Quit while you're ahead" but I'm trying to make it sound like fresh advice that I just thought of) If you do this, your audience will applaud more eagerly and with greater joy and probably remember your speech as being funnier than it actually was. They are happy. You will be happy. That's the main thing.
I mention this because recently, I've been writing one or two scripts and had notes about the ending. One or two of these notes say 'can we have an extra joke at the end'? (Notes which say 'can we have more jokes please' are annoying but ultimately worth having because it reminds you do your job and write funny bits. If you don't want to write funny stuff you're on the wrong floor.)
The temptation is to keep coming up with extra joke and epilogues and more bits and extra pay-offs for running jokes - until you end up with two or three pages of this stuff with jokes and bits that the audience frankly don't care about all that much. Once the hero has succeeded - or failed in a pleasingly comic way - wrap it up fast. With in a page or two. Give the audience the chance to catch their breath. Pay off a running joke. Then cue music and roll the credits. You'll be finishing the show a split second before the audience are wanting you to and they will cheerful about it.
But listen at me prattling on. Actually, there was this one best man's speech I heard about in which... oh yeah. Quit while you're ahead. See ya.