Ask students to write two scenes: In the first scene, they should use an active scene with action and dialogue, which also includes a brief flashback told within the scene. In the second scene, they should write an entire scene in flashback. This is to gauge the students' level of expertise. Hopefully, the students will have some previous experience in writing scenes. Regardless, every student can learn these techniques. The "Bible" for writing scenes and flashbacks is Jack Bickham's book, "Elements of Writing Fiction: Scene and Structure."
Evaluate the students' first exercise.
Show students what constitutes good use of flashback technique, and what constitutes poor use. Current convention dictates that flashbacks within an active scene are short. Longer flashbacks require their own scenes, and are usually written as a sequel to an active scene. A sequel often involves reflection upon the actions in the previous scene. A sequel is an excellent vehicle for flashbacks.
Ask students to write an active scene, which includes a long flashback within the scene. Ask them to rewrite the scene, cutting most of the flashback, and leaving only the essentials. Emphasize that readers will stop reading a book when there is little action or dialog.
Show students how to transition between 'story time' and 'flashback time' within the same scene.
In 'story time,' students expect the action to be the present day. In 'flashback time,' if you have a brief flashback within an active scene, you need to use the past-perfect verb tense to indicate that the time has shifted out of the present day and into an earlier time.
Ask students to write a scene that illustrates this principle.
Ask students to write another entire scene told in flashback. In commercial fiction, this is generally done via a sequel. The sequel is usually told from the point of view of a character other than the protagonist. In a romance novel, the point-of-view character is usually the heroine. In a flashback scene, the point-of-view character might be the hero. This tells the reader what the hero is thinking, something the reader usually doesn't see when the point-of-view character is the heroine.
Ask students to write another short flashback within a scene. Then ask them to write a flashback scene that directly follows this scene, with a character other than the point-of-view character. For an entire flashback scene, it is not necessary to use the past-perfect tense, as the reader will sense that the character is going back to an earlier place in time.
Read the students' essays to assess how well they understand the principles you're teaching them.
Emphasize that learning is a process and that everyone can learn these simple techniques.