SHOW, DON'T TELL
It can be tempting to simply list examples of a funny idea (once you've hit on one) in your improv scenes. SHOW, DON'T TELL reminds us that it is almost always funnier (and more fun) to put those same ideas into action.
Say, for example, you are in a scene that centers around the idea of a "Secret Relative". You've laid out that your Aunt only comes around when they know very few people can see them, sort of like Snuffleupagus. Well, you might simply describe this situation to your incredulous scene partner, with lines like, "Yeah my Aunt was tapping on my bedroom window late last night. She wanted to take a photo with me to celebrate my 20th birthday, so I sure am sleepy." While this is funny, wouldn't it be funnier and also more fun to initiate the scene by tapping on the window as the Aunt herself?
The powerful difference between listing a funny idea that occurred (or will occur) offstage and putting that idea into motion is the essence of the saying SHOW DON'T TELL.
Good exercises to bring up SHOW DON'T TELL:
Tag Out Runs