Knowledge
A good improviser knows stuff. A lot of stuff. They not only need to be book smart but they have to have a brain that is hungry for information and for knowledge. That's the kind of brain that I want to improvise with. I don't care what kind of improvisation you practice, your quest for knowledge should be never-ending. It's this quest that ultimately makes you a better and funnier performer. Pursuing knowledge trains your brain to not only remember information but to also make connections and find patterns. I don't care where you pursue your knowledge. If your thing is reading Entertainment Weekly and People every week, fine, but just let your brain absorb that information and then share that information with me on stage. The most immediate effect is that by putting this information in your head, it's immediately becoming part of the hive mind of your ensemble. If I'm lacking information on the latest pop phenomenon, I know that if it's in your head...