Kick the Can, Marco
Someone in the group shouts “Let’s play…” and then names a totally made-up game. Everyone says “Yeah!” before launching into the game as if they know how to do it.
After the game, ask everyone to tell you the rules. A brand new game has been invented on the spot!
Play this a few times until they can spot, define and play the rules as they go along without talking about them.
This is a fantastic game to help people get used to the idea of finding games in scenes.