Time needed: 1 to 5 min
Why? Telling a story themselves encourages students to articulate their thoughts and make their inner world accessible by narration.
When? Once a lesson would be excellent.
How? First a topic of the story is discussed and agreed on. Then your student tells the story. No need to be funny. Nevertheless some humor is fine.
Any risks? Make sure every student gets the chance to tell a story. Some storytellers are better than others. Some need more time and concentration. Some need to prepare, others won‘t. In any case create a setting which enables your students to listen carefully. Storytellers should only talk when audience is listening.