This is an excellent little warm up that I’ve found on improvencyclopedia.

Description

Everyone in a circle. There are 3 things a player can be:

• An alien: hold you index fingers up next to your head, as little antenna`s and say `Bleeb bleeb`, bending inwards into the circle;
• A cow: bend forward, hold your right hand on your tummy and go `Moooo`
• A tiger: push your right hand forward, imitating a claw and roar.

On your sign, every player decides to become one of the three. The idea is for everyone to become the same, which obviously won`t be the case, the first time. We re-do this until everyone is in sync.

Variations 

Invent your own animals (or things) and let players become juke boxes, birds, whatever.

Play `majority wins`: animals/things that are most in the minority drop out.