I've had a lot of fun asking it to generate stories, and then imposing new details or constraints on the story. Asking it to include dialogue and stage directions often makes for more interesting output too.

Then you can do weird stuff like have one character only speak in French, or two characters always speak in unison, or give someone a stutter.

Some constraints didn't always work. I tried to have a character always vehemently disagree with anything anyone else says, but it would only disagree once or twice.