Flashbacks are very powerful ways to improve a screenplay’s storyline
Using flashbacks generally has one major advantage this is that it allows past incidents to be dramatized in all their impact instead of just recounted verbally
It helps if the audience really wants to know the information contained in the flashbacks
In some films after an opening scene, an entire story is told in flashbacks; the first scene poses a very clear question and hooks us into the story immediately.
A potential downside of a flashback could be that the ending of the story is already known to the audience.
This risk is balanced, however, if the difference between the end situation
and the development of the flashback story creates a strong sense of dramatic sarcasm.
Also, a clever writer can create the illusion that the story might as yet end differently. In Carlito’s Way, for instance, we know from the outset that Carlito is doomed. Yet, near the end of the story, he triumphs over his enemies, and we start to hope that the opening scene was some kind of dream or fantasy. When tragedy strikes, it does so from an unexpected, yet logical, direction maximizing the impact on the audience
One of the main rules of a flashback is that if we close in on the face of one character as the flashback begins, it will represent his or her memories.