Every once in a while when you are improvising, you should do something on stage that surprises you. Start telling a story in the middle of a scene without knowing why. Just start speaking. Make it about something that hasn’t come up yet. The first few sentences should feel like a non-sequitur. You should have no idea how it connects to the scene so far. Before you finish the story, you will figure out why you are telling it. And if you don’t, your scene partner most likely will make a connection for you.
The key is to make your subconscious brain do some work. Your mind is terrific at making up little stories to justify your actions in the real world. For every conscious decision you make, your subconscious mind is probably making dozens of choices, maybe hundreds. Harness that power in your scenes and you will find it almost always improves them.
There is a place for carefully considering your scene partner’s moves and providing thoughtful responses. There is also a place for impulsive moves, gut reactions and non-sequiturs. Real life conversations are filled with surprising twists and turns when viewed from the outside. Your scenes should have them too.