Since most jokes we know have been around the block a few times, it is sometimes helpful just to recite the punchlines. That way, you get to remember the joke without going through the trouble of hearing the set up. What's more, you get the pleasure of reconstructing the joke. Finally, if you don't know the joke, it can be fun to imagine the set up. This is a great way to recycle the oldies but goodies.
Here are some examples:
"He was charged with transporting gulls across a state lion for immortal porpoises."
"You didn't get one?"
"It's the cat!"
"I wanted to know whether to bargain him down or steal it."
"I've seen shaggier."
"Look who thinks he's nothing."
I enjoy ethnic humor now and then, but I like to use rare ethnicities that aren't likely to be represented in the room when I tell the joke. "An Inuit walks into a bar with a parrot on his shoulder. The bartender says, 'That's neat! Where'd you get it?' The parrot answers, 'In the Yukon. They run wild there.'" Damn. It's even funnier with the Inuit in it. It's also fun to substitute ethnicities so as to transfer stereotypes in novel ways. "What did the Sicilian yell at the football game? Get the quarter back!" "How did the Soviets defeat the Germans. They marched in backwards, and the Germans thought they were leaving." "What's the most confusing holiday in Israel? Fatrher's Day."
Lawyer jokes are ten times funnier when you apply them to novel professions, such as nurses or hostel workers. "What do you call a thousand hostel caregivers on the bottom of the Hudson? A good start."
See how much mileage you can get out of your old jokes with just a few minor changes?