From Janice Hardy’s Fiction University:
A character’s history is important, but not enough to bog down your entire story to hear it.
Along with adverbs and telling, I think backstory completes the unholy trinity of writing. So much so that agent and writing guru Donald Maass advises writers to cut any backstory in the first 50 pages.
But backstory does have its uses, and sometimes, it’s critical to know that history.
Even if it’s not critical for the reader to know it.
In some genres it’s more of an issue. Fantasy, science fiction, historical—any genre where the past and the history of that past strongly affects the current plot and the motivations of the characters. Doubly so if the antagonist is the one with the past that’s come back to haunt someone, since you don’t always see the antagonist’s POV.
One of my WIPs has a major event that happened decades ago, but this event is the trigger for all the present-day plot events in the story. I knew basically what had happened in the past, but I focused more on what my protagonists were doing/uncovering and chose what parts of the antagonist’s plot to use based on them, not what had actually happened.
By the time I was done, I wasn’t happy. The mystery part wasn’t as strong as I knew it could be, because I hadn’t spent enough time on the backstory. If you looked too closely at the plot, things didn’t quite line up, and questions were left hanging.
The more you thought about the story, the weaker the story got. Not a good thing.
So I went back and wrote the backstory.
I drafted a rough synopsis that described that past event and what happened. Why the characters did what they did and the ramifications of those actions. When I was done, I did the same thing with my antagonist. Then, I did it with all my major and supporting characters who were involved in it, no matter peripherally. One character was nine years old when this happened, but after doing this, I realized the event had a profound affect on who he was that made his character much richer and more interesting.
That’s a lot of summarizing and a lot of backstory, but afterward, I knew how all the pieces fit and those plot events that felt shaky could now be made solid. I knew why folks did what they did in the present day plot, even if they weren’t the POV character. I had secrets non-POV characters wanted to avoid, which gave me all kinds of great fodder to use to up the mystery, the tension, and use for plot.
Link to the rest at Janice Hardy’s Fiction University