My big problem with the “spontaneous write a story” exercise is having to come up with a plot/character idea on the fly. Any ideas on how people do this, either for writing short stories or improv-type stuff?

Once I have a novel framework, outline, or other harness to work from, maybe I won’t have to worry about generating random ideas. I have a pretty good idea of the setting (contemporary) but I will still need plot and character development.