The most important thing to remember... Flashbacks should not be used unless there is absolutely no other way the story can be told. Flashbacks carry a built-in disadvantage to even the best of written stories, because it stops the story. A flashback is about something that has already happened. It's over and done with so the flashback lacks immediacy.
There are 3 advantages to having a flashback in a story...
- helps establish character motives
- fills in events of how the original current story came about
- fills in critical information that happened years earlier
If a story must hold a flashback there are 3 ways to maximize the advantages of a flashback...
1. Time travel done right
Every flashback should follow a strong current story scene. Flashbacks should never start a scene. Before dropping the past onto the reader, the current story must be established first; otherwise, the reader will become invested in the flashback and not care about the current story.
2. Orient the reader at the start of the flashback in time and space
Make sure that it is made clear that the story is moving backwards in time. Give a clear indication at the very beginning what is happening to avoid throwing the reader into confusion and frustration. There's nothing worse than reading a story and not being able to figure out where in space and time the story is supposed to be taking place.
3. Use verbal tense conventions to guide the reader in and out of the flashback
Conventions through verbal tense can be used to "signal" both the start and end of a flashback. This sort of thing is subtle and may not be noticed by the conscious mind of the reader, but is very effective in guiding the reader properly in and out of flashbacks. This is the best way to help eliminate flashback confusion.
Example: Let's say you are writing a story in pasted tense (that's my preferred style of writing). That means the first few verbs (usually the first 5 verbs) used in the flashback should be perfect past tense (had, had been). Then switch back to pasted tense. When you are ready to end the flashback switch back to perfect past tense for another 5 or so verbs. Once back in the current story, you return to using past tense verbs.
Are you confused yet? Here's a shortened version I made to help me keep it straight...
current story (past tense) + beginning of flashback (perfect past tense 5 verbs) + middle of flashback (paste tense) + end of flashback (perfect past tense 5 verbs) + return to current story (past tense)
What if a story is written in present tense? Then you would use past tense verbs instead of perfect past tense verbs.
Here's an example of a switch from a present tense story to flashback from Suzanne Collin's Hunger Games...
"We don't speak. Our real interaction happened years ago. He's probably already forgotten it. But I haven't and I know I never will...
It was the worst time. My father had been killed in the mine accident three months earlier in the bitterest January anyone could remember. The numbness of his loss had passed, and the pain would hit me out of nowhere, doubling me over, racking my body with sobs. Where are you? I would cry out in my mind. Where have you gone? Of course there was never any answer."
If flashbacks are used, it should be done sparingly. Flashbacks should never occur back to back. Strong scenes should separate each flashback scene.
There is an acceptable form of story that uses flashbacks to tell a story and that would be a "frame story". This story can be any length (from short story to novel), which begins after all the action is over. The protagonist or author announces that they are going to tell a story and may even give out the entire outcome at the beginning of the story. Example of this type of stories are True Grit by Charles Portis and Water for Elephants Sara Gruen.