Yes, let's

A great warmup for group collaboration and to practice saying yes especially for improv beginners.

Everybody walks around the room. One player suggests to do something, i.e.: "Let us hop on one leg.".
The all players shout: "Yes, let's!" and everybody hops on one leg until another player suggests something else.
Sometimes inadvertently even little stories are created.

Examples:
"Let's swim like a fish in water."
"Let's stumble and fall down."
"Let's laugh sheepishly."
"Let's pretend we are coming too late for work."
"Let's dig for a lost treasure."
"Let's recite the alphabet backwards."