Well, I say new, it's from Viola Spolin's book which was from the 1950s or early 60s, but I found it really effective on Saturday and in fact one of the most complete character exercises I've led.
1. Get four actors up on stage, in a line facing the audience.
2. Point to one and they repeat an emotional or expressive statement, for instance "I'm really happy, I'm really happy, I'm really happy."
3. They stay relaxed as they are saying it. Pick up and point out their changes in body as they say it. For instance - "your eyebrows have raised, you hop up when you speak, you're smiling, you sway."
4. When they have received some physical pointers shout 'Hold It' and they keep that character. Whatever they do next their point of concentration is on holding the new physical characteristics.
5. Repeat for the other actors.
6. Put them through a series of five or so completely different scenes, with them keeping the original characteristics, physicality and attitudes. Give them complete where, who what in each scene so you can focus on the effect of character.
You can later repeat the whole thing but without pointing out the changes of physicality, so they can discover it themself.
It doesn't matter if the emotional statement is based on how they are actually feeling, or if it's come in from the outside, as either will change them and generate a character.
Doing a sequence of scenes rather than just one is excellent as it isolates character and demonstrates the effect of character on scenes.
It's a fascinating game as it strongly shows the connection between inner life and outer physicality. The actors were surprised how strongly they felt in the scene, and how much just saying a line of emotion changed their physicality. Sometime there is debate in impro about whether to act from 'the inside out' or the 'outside in', but actually doing both at almost once happens in this game and is highly effect.
Thanks to everyone for taking part.