Opening the book…
The mind builds a world from specifics, not summaries, and one exact, chosen detail will do more than a paragraph of general description. Tell me the tax collector wears gloves so he need not touch the coins of the poor, and I know more about your society than a page on its class system could convey. The telling detail works because it implies, letting the reader's imagination supply the surrounding whole from a single vivid part, and imagination summoned is always more powerful than description imposed. Vague, comprehensive description asks the reader to do nothing and gives them nothing to hold; the sharp particular hands them a key and lets them open the room themselves.
Reach for the specific over the general everywhere: not a market but the smell of the fish stalls at closing, not a proud people but the way they refuse to sit while a guest stands. Choose details that carry more than themselves, that imply a history, an economy, a whole way of life, and cut the generic ones that could belong to any world. Trust the reader to extrapolate, and resist the urge to explain what the detail means. When a passage feels flat, do not add more description; replace three vague sentences with one exact object, gesture, or smell, and let it do the work of all of them.
Detail can be overspent; a world where every noun drags a symbolic freight becomes exhausting, and sometimes a plain sentence should just move the reader along. Pacing needs stretches of ordinary prose between the vivid strokes. The craft is knowing which moments deserve the telling detail, not lacquering every one of them with it.