Many beginning writers feel the need to write a couple of pages—or <sigh> a couple of chapters—of narrator backstory. Sci-fi and fantasy writers suffer from this compulsion more than most, probably because they have spent time and effort building an entire world (or universe) of creatures, planets, civilizations, technology, rules of magic, and so on. They want the reader to be familiar with these concepts before the plot begins.
Now that I think of it, writers of political thrillers often think that if readers don't know how the current state of affairs came to be, the reader will be lost. They start with pages of narrator exposition. Editors often refer to it as narrator infodump.
Let's look at how to start a story without narrator exposition.
First, a slight digression. The most common cliché start by new writers, especially teen writers, is with their main character in bed. Acquisition editors groan, and many won't read any farther. A typical beginning would go like this:
The alarm clock goes off. Debbie gets up. She looks in the mirror (so that author can describe her to reader, also a common device that makes editors wince). She gets dressed, goes downstairs, has breakfast, says goodbye to Dad and her little brother, then leaves for school. She goes to English class, almost falls asleep. In period 3, she breaks up with her boyfriend.
Well, the story should have started in period 3.
The writer thought it mattered to the reader to see the home life, hear Debbie banter with her Dad at the breakfast table, and discover that Debbie has a younger brother. These facts may be important to the plot and to Debbie's character development, but might not be needed yet.
If the writer showed us that stuff through action and conversation, though, I have to give her partial credit. Many writers would have had their narrators fill us in.
That brings us back to narrator infodumps. Suppose the story involves Debbie's continuing turbulent relationship with her boyfriend, Ari. The narrator could have spent many paragraphs telling us when they met, what she first thought of him, how he won her over, how he took her to a school dance and vowed to love her forever, etc. If that is the story, then okay. Tell it. But if it's what the writer thinks we need to know before the real story begins, then there are better ways to do it than narrator infodump.
Suppose the story starts later in the day, after the breakup. Debbie and her friend, Jessica, are at the corner restaurant. Are you really going to dump him? Jessica asks. Debbie nods. But you've been going together since the summer, Jessica says. He took you to the dance. You said it was wonderful. A dazed look comes over Debbie for an instant. Then she slams her fist on the table and says something like, "That jerk. Eternal love. For ever and ever, he promised. What bunk!"
I didn't format that like a real conversation; I hope you caught the gist of it. Did you see how the information about when Debbie and the guy met, and his vow of undying love came out without a narrator filling in the backstory ahead of time?
Let's take another example. Suppose Debbie was an only child, a fact that is important throughout the story. Did a narrator have to tell us that? Imagine, instead, Debbie and Ari are arguing and he tells her to get a grip, talk to someone about her problems. Debbie comes back with, "Easy for you to say. You've got brothers and sisters." Voila. She's an only child and neither she nor a narrator actually said it.