If you don't want to wait for us to publish additions to this lesson, go read Keith Johnstone's books about improvisation. Anything we say in this lesson will probably turn out to be a variation on what Johnstone has already written.

Impro (1979)
This book is life-changing.

Impro for Storytellers (1994)
Extends and expands on Impro. Encyclopaedic. Not the kind of book you read end to end.
You'll probably find other books on improvisation or narrative helpful, but Johnstone's work is seminal.
In fact, even if you do want to wait for additions to this lesson, you should go read these books.