General advice to fiction writers is to think about particularized details that give the reader an insight into character. For example, you can say, "She likes chocolate," but almost everybody likes chocolate. It's far more revealing to say, "The only chocolate she will eat is imported from Mozambique." That immediately gives you a little sense of her character—not much, but it's a start.
When you invent a fact in a story, it becomes imaginatively true, as long as it doesn't contradict the story's logic. This is one of the great mysteries and secret delights of writing fiction. As Nathanael West* wrote, "Possibilities became probabilities and wound up as inevitabilities."
When you start to make such lists, you discover a principle of inner consistency. Suppose the list gets long enough, the inventory first of possessions, then of personal appearance, including beauty or handsomeness, and finally an appraisal of personal qualities. In that case, you realize that some items belong on the list, and some things don't belong there, and you take out the ones that are wildly inconsistent with the rest of the list.
Make a list about an imaginary character named Harold. You will discover, eventually, that some of your facts don't belong on your list: if Harold belongs to an Alaskan hunters association and drives a Hummer, he probably doesn't spend the rest of his time playing the viola, working for Earth First!, and translating the poems of Jorge Luis Borges. He might, but you'd have some explaining to do.
Fiction is about filling the vacuum of our knowledge, which is why fiction loves inventories and lists.
You begin to discover something else when you make lists like this. You discover that you can say "She is brave" as an important statement that feels unsubstantiated, thin, and unsound until some proof is offered. "She is brave" is a claim about an inner quality, as is "He is timid." You can make a lot of claims like this. Still, sooner or later, you have to establish their validity unless you believe what Lionel Abel said about Prince Myshkin—that some people are intrinsically good or bad without anyone thinking they are.
But how, on what grounds, would you believe such a thing? Claims about character are like promissory notes or assertions in court, and they require actions or evidence to back them up. You can say, "Over this dresser, there on the wall of his bedroom at home, this teenager has a poster of the band Grätüitöüs Ümläüt." Or: "This young adult male has a tattoo of a roaring lion on his right calf." These assertions are not claims; they're statements, markers, about possessions and therefore are parts of inventories.
When you start to write fiction, you can help yourself by noticing the difference between making a claim about a character (that is, what a character is) and making an inventory (that is, what a character has). Every claim will sooner or later have to have some proof. But statements, inventories, start to build a world immediately. They are the proof. And notice this: you can describe characters in absentia, sometimes, just by describing what they've accumulated in their rooms. Tell me what those particular teenagers have in their rooms, and I will begin to tell you who they are.
It's the nature of fiction to love inventories and lists. Fiction's subject matter is often related to sheer accumulation. Fiction loves to pile things up, the way bricks and mortar morph into a structure.
Writing fiction is about accumulating details—details about the setting, clothing and behavior and actions and speech patterns, and all the rick-rack of objects we surround ourselves with. If you don't like amassing this barge load of material, you may not be comfortable with fiction, or at least realist fiction, which tends to fill up the page with accretive details.
An inventory of objects surrounding characters helps to define those characters and, perhaps, be an aid in measuring the size of their fall. But the inventory is typically unable to give a sense of the importance or significance of that fall; other means must be found for that. Some materialists are corrupt, but others may be innocent. When their possessions are taken away, we learn which are which. What sort of person will you be if I take away all of your possessions? It's unlikely that you will be the same person you are now.
*Nathanael West (born Nathan Weinstein; October 17, 1903 – December 22, 1940) was an American writer and screenwriter. He is remembered for two darkly satirical novels: Miss Lonelyhearts (1933) and The Day of the Locust (1939), set respectively in the newspaper and Hollywood film industries.