Before you begin to write, familiarize yourself with the era in which your work is going to unfold. Historical forces (real or imagined) are as important as any single character.
That's because people are moved by their place in time. Circumstantial motivations and reactions are defining. Understanding the when helps explain the why.
Your era may be familiar (World War l, the Depression) or may require a more granular world-building -- the impending drowning of a small town to make way for a hydroelectric plant, for example. But the details matter. In the latter case, the flood will have vastly different effects on each of the characters, shaping their existence, actions and storylines. Everyone is about to go through the same thing -- but to varying ends. The old woman who rents above the barbershop faces homelessness while the area's largest land-owning businessman, the mercenary owner of a 50 acre for-profit drug rehab center, is all set to make (another) killing once the flooding starts
The novel, let's call it Water, might open with an announcement taped to the door of the high school gym outlining the various closures and coming terminations of municipal services that will culminate in the community's extinction. The looming event might be nothing more than a motif or framing device (captured in snippets of convo throughout the novel at the coffee shop or in the lobby of the all-but abandoned daycare center) but it's there, a backbeat of the narrative, molding the concerns and actions of your cast.
"Where are you going to go? How about your wife? Have you found a facility for her nearby?"
The main plot of Water may in fact be a tragic love triangle between the town's guidance counselor, principal and cheer coach but it might end with a description of a body breaching the surface of the new dam. Tying time and throughline together.
Doing homework about the period is worth it. Inaccuracies are unforced errors. The provision of true historical details offers both color and satisfying filler. It's worth it to do a little research so as not to turn off your audience with anachronisms.
I'm not saying you have to be completely anal but having somebody purchase a Talking Barbie for their kid to celebrate the end of World War ll is just wrong. (C'mon man.)
If you're writing about the 60s bring in interesting details emblematic of the time. Just not too emblematic -- over-used elements reek of one of writing's deadly sins--cliche. (See: incense and Patchoulli Essential Oil.) The days of civil rights, women's lib and communes were rife with many other features. If you are setting a novel or back-story in a 60's commune what was the impact of its freewheeling, open-door policy? Might one too many drifters have been invited in, changing the trajectory of a lonely little boy who slept on the couch in the front room? Even mundane things like how chores were divvied up are informative. Was there a Utopian ideal of all co-habitants helping each other -- or did regular resentments rear their little heads over the dirty dishes in the shared kitchen?
Mid-last century, there was widespread, overwhelming school-triggered dread caused by recurring under-desk atomic bomb drills. And tapioca flavored S&H green stamps that a small girl may have licked and carefully stuck inside her own little booklet to save up for a dollhouse with room-specific furnishings pre-stamped on the metal walls. If her big brother wanted a dollhouse, too, he would have been directed towards collecting the stamps for a more 'gender appropriate' fishing pole. Of course, this could either be 1964 -- or modern day anti-Woke Florida-- but fateful, just the same.
On the flipside, it's possible to way overdo. I once listened to some of a very long mystery in which the author spent a significant amount of time basically inserting Google lists from everything 1970s. It was so absurd I was laughing by the time I threw in the towel. (I didn't even bother fast-forwarding to uncover who the murderer was, which in my dotage I've started to do. I just didn't care.)
Even if you're going for a Hemingway-esque economy of style (known as the Iceberg Approach where many things take place beneath the surface of your story, unsaid and undescribed) having a good grasp of what's going on down there keeps you in control of the narrative above ground.
Let's say you have an unadulterated asshat of a villain, a guy who treats women with vulgar disregard and hums with a constant drone of low-grade rage. Now imagine this guy is a member of some religious police state. Or an American incel longing for one. He's egged on by his web cohort. Though his conformity to social norms doesn't excuse his reprehensible beliefs it's important to convey whether the dude is a lone wolf misogynist or a peer-pressured believer in TradWives and child-voiced women. I mean the end result may be the same but contextualizing it is important.
Conveying information about the literal 'when' can be either straightforward incident report or stealth. Obviously there's the chapter heading dateline, which you have to admire for its simplicity, but slicker methods abound: Her godson was born in 2000 so she always knew how many $5's to stick in the card, 24 this year. You can set the time with music, playing Casey Kasem's Top 40 in the background of each chapter. Or there could be a radio homage to the 60th anniversary of the Beatles' arrival in the U.S. Clues like that provide alert readers with the same opportunity for a charge they'd get from plugging in a jigsaw piece or spotting a parking place.
Names, too, provide historical markers. (See: Ashley Madison -- the cheating app adorned with the most popular girl handles of the 2000's.) Um, how sick is that? But it wasn't called Bertha Gertrude for a reason.
All of which is to say that knowing the era of your work is almost as important as knowing your characters. Maybe not the protagonist but definitely an overbearing parent or philandering spouse.