One of my favorite games to play with new improv students is "Another Choice". The game has two actors and a conductor. During the scene at any time (when appropriate), the conductor may say "another choice" and the actors will have to repeat their previous lines, but change the last one. For example:
Actor 1: I'm bored, why don't we go on a drive to pass the time?
Actor 2: I remember the last time we drove, it took forever for us to get home.
Director: Another choice.
Actor 2: I remember the last time we drove, somehow all four of our tires popped simultaneously.
Director: Another choice.
Actor 2: I remember the last time we drove, somehow we got into a wacky race against cartoon characters.
Actor 1: Yes, but we made a lot of interesting friend. Even if a few shot at us I still consider that a win.
Etc. As you can see this forces the actors to thing creatively and explore new options. And usually they get zanier and more interesting the further it goes on. This is just like stretching your muscles, in future games the actors will be able to explore new options in their scenes.
The other day at practice while we were playing Another Choice I noticed a new actor was speaking well, but her movements were very lively or animated. That's when I realized an excellent application for this game which I named "Another Action". The rules are the same as Another Choice, but instead of changing their line, they have to change what their body was doing during the scene.
For example if our two actors were in the car driving and interaction like this may take place:
Actor 2: Just please drive safely this time.
Actor 1: What does it look like I'm doing? (Mimes turning a wheel patiently).
Director: Another Action.
Actor 1: What does it look like I'm doing? (Starts turning wheel hectically.)
Director: Another Action.
Actor 1: What does it look like I'm doing? (Pulls wheel off of dashboard and turns it in front of Actor 2's face.
Actor 2: Well if that's how they taught you in Driver's Ed I guess it will have to do.
With these two games we can stretch an improviser's creatively and movements, so they make great games to start a practice off with. And if you're feeling devious, it could be fun to mix both of the games together!