This can be done in pairs as an exercise or in front of an audience.
It's a scene where every line of dialogue, after the first, starts with the words "I know".
That's it.
It's a really powerful technique even though it's really simple.
It's an alternative to YES AND (without the problems of negotiating consent).
It focuses your world down into detail and specifics. By setting your default to I know you are automatically validating each and every idea your scene partner has, anchoring them as commonplace reality.
When you enter a scene, your character knows more than you do. As an improviser, you are stepping into a blank space - you don't know who you are, where you are or what you're doing. You are trapped between reality and fiction. Your character, in contrast, knows everything about the scene - they know who they are, they know who they are with, they know where they are and why they have come there. We want to close this knowledge gap as quickly as possible. And so often we put questions into the mouths of our characters - questions they wouldn't ask because they obviously already know the answers.
Who are you? Where are we? What was it you just said I wanted?
It's a crude strategy to get the improviser on the same page as the character. And it's clunky as all hell. Far better to just assume knowledge of the situation.
Make assumptions about your scene and, as there is no objective reality, by the power of improv they will be transmuted from mere speculation into concrete fact within the world you're creating. You get to the same place of agreement but you don't have to ask question or put the burden of creation on your scene partner. Lovely.