Tina Fey said this quote

“ The second rule of improvisation is not only to say yes, but YES, AND. You are supposed to agree and then _add something of your own._ If I start a scene with 'I can't believe it's so hot in here,' and you just say, 'Yeah...' we're kind of at a stand-still. But if I say, 'I can't believe it's so hot in here,' and you say, 'What did you expect? We're in hell.' Or if I say, 'I can't believe it's so hot in here,' and you say, 'Yes, this can't be good for the wax figures.' Or if I say, 'I can't believe it's so hot in here,' and you say, 'I told you we shouldn't have crawled into this dog's mouth,' now we're getting somewhere. ”