To prepare, I get one sheet of paper for each student and at the top of each sheet I write an opening sentence. When I've finished writing the opening sentences, I give the students a single sheet of paper each and tell them to read the sentence that I've written and then to write a sentence of their own to continue the narrative. When they've done this, they pass the paper to another student who will write one more sentence before passing it on. She soon fell in love with the gardener, married, and had some interesting children. When the students have finished, I collect the narratives and check that they are understandable.
Pictures are a good starting point for writing narratives.
I then tape these to the blackboard and tell the students that they should choose a picture of one person and try to write a narrative imagining that they are that person. They have to concentrate on details like job, hobbies, whether single or married, children, and so on. I also tell them to avoid describing the person's physical appearance and to use first person singular pronouns throughout. As there is no description of physical features, the students have to listen closely to try and identify the right person. Using the first person helps to make the narratives sound authentic and convincing.