Don't Think Twice, Mike Birbiglia's movie about improv + improvisers + an improv group, comes out in July. Keegan-Michael Key (of Key & Peele, of Second City) is in the movie, and a video's been making the rounds of him talking about improv. He says:
"People think that improvisation is moving forward. What improvisation really is, it's walking backward. While I'm still looking you, I'm going, I'm here with Sam Jones. As I back up I see there's a light there. What's the light? Oh, I'm on a set. Sam Jones must be a person who works on a set. I keep backing up, I see this chair, I see that chair, I go, Oh he's an interviewer! I keep backing up to Nate -- That's the soundman! What's this room? Oh, it must be a small show! It's backing up that gives you discovery. As you back up, you can create a larger worldview."
He goes on to talk about playing game (or, "the game of the scene"), but that's a whole ball of spiders that I don't mean to get into today. My ears perk up when he says discovery. He's talking about asking yourself, "If this is true, what else is true?" If you are talking to a man and surrounded by lights, you are on a set. If you are on a set and talking to a man and there are two chairs facing each other, you are in an interview. If the other man is asking you questions, you are the one being interviewed. If you are being interviewed, you have done something worthy of being interviewed for.
And that can be a scene! It doesn't have to be a complicated crazytown premise with the cleverest of wordplay and broad characters. If you and your partner have established a reality and lived -- fully! -- in that reality for a few minutes, then you have created a successful improv scene. And all you had to do was be there together. None of that is invention -- it's already there when the scene begins, you just have to see it.
"Don't think fast," Key says. "Just listen to the last thing (your partner) said."