“…This one’s eating my popcorn!”
Punchlines work best at the end of the joke. This goes for a verbal punchline, a visual punchline, a story punchline, whatever. Set it up with the audience, let them build up a little interest in the Anticipation Bank, and then deliver the punchline.
It’s a trick I picked up doing stand-up and improv. It’s weird to think that there’s a mechanical aspect to comedy, but it sure seems to work.
And by “punchline,” I include non-comic things as well. Even in a dramatic moment, unless you’re very, very Memento-style clever, there’s a “punchline,” a place where something is revealed that makes sense of what you’ve already seen in a way you didn’t expect.