"The piece of improv advice that seems to have stuck with me and the one I continually go back to was given by Armando Diaz in a class early on. After a stretch of particularly horrible scenes, he stopped us and in an unusually raised voice said "It's very simple! All improv is is..." and he took his two hands and made them as if they were two people talking to each other. One hand said in a tone "rawr" and the other, in a different tone, responded "RAWR."
And that is all improv is. It isn't saying the funniest thing. It isn't predicting the scene before it happens. It is responding honestly to what is said in the moment."