You’ve done all the research. You’ve mapped out (literally perhaps) your new world, and have crafted a story worthy of a Dragon, several other awards, and lots and lots of Benjamins*, but your alpha and beta readers say, “I’m just not feeling it. I can’t see your world.”
What went wrong?
Details. You need enough detail to make the world real, especially real to the characters who live in it, but not so much that the reader drowns. This is, alas, no longer the 19th Century and we can’t go on for pages and pages about fashion, food, or other things. Unless it is critical to the plot, or you are writing a milieu novel, and even then, see “the problems of the unrestrained info-dump.”
Let’s say you have a fantasy set in a world with a tech level of late Imperial Rome. Or Autumn in the Warring States period in China. You’ve described the buildings, and the economy, and what the characters look like. What’s missing that might bring things to life, including your characters?
Sound. Smell. Taste. Touch.
Smell in particular is very evocative, can be atavistic, and a whiff is sometimes worth a thousand words if used properly. Unless you have sanitation magic, your city is going to have lots of smells, most of them less-than-pleasant to modern noses (those belonging to your readers). Your characters might be more matter of fact, identifying the sharp whiff of concentrated ammonia (stale urine) with the tanning distract, or the cloth-finishing businesses. Oh, the wind is from the south because I can smell X. Smells are also seasonal, both because of heat (low water plus high heat equals “pew!”) and because of foods, crops, and fuels varying over time. In a pre-modern setting, smoke will always be present, unless you have magic to keep it away or don’t cook in the conventional manner. Is it wood smoke, nasty half-rotten-wood smoke, soft-coal smoke, or something else? Do you smell meat or frying? What about incense, or burning grass or old burning hay? Does a south wind bring metallic scents from the smiths’ workshops? If not, why? What’s going on if a familiar smell goes away?
As Kipling (PBUH) said, “Smells are surer than sounds or sights/ To make your heart-strings crack.” (“Lichtenberg“)
Taste can be obvious (good or bad food, rotten food), the taste of blood from a mouth injury. Or more subtle, like water in a spring that’s a little odd, or meat that doesn’t taste as advertised. The textures of foods are also important. Real stone-ground flours, unless they are sifted very, very well, are a little gritty. Your noble sniffs and grumbles to herself about the quality of the bread. It tastes fine, but the texture tells her that the flour has not been sifted as well as her rank requires. Or that someone is sparing flour by adding fine-ground cornmeal.
Sounds are obvious or subtle as well. Why didn’t the dog bark in the nighttime? The birds suddenly begin to sing. Is this good, or does it mean that the forest spirits are passing through the woods and that everyone needs to cover their eyes lest they see the forbidden? In the darkness of a mine, sounds seem louder, but where are they coming from? What was that creak, that water sound?
Is fabric slick, waxy, soft, rough enough to snag easily, lumpy, tight-woven and smooth, knitted? Is there a little burr on the blade of the knife that must be ground away? Is that a clue to a murder or a reminder of a nasty fight? Has the mule always had that lump under the skin on his shoulder or is it a warning that the harness has caused problems, or worse? What is the texture of the soil that the scout is feeling and sniffing?
Obviously, you can go overboard. I have excised page after page of clothing from certain books. Or you can have excessive detail to comic effect, as a young man goes on and on and on about the virtues of his enamorata, while everyone else rolls their eyes and giggles behind their fans.
Also important, sensory detail can reveal a lot about a character. Rada Ni Drako depends a great deal on smell, and notices them and comments on them. But her color vision is poor compared to humans’, unless she is close to the object. Odile in Peaks of Grace describes every sensation… except visual images. The Staré communicate with pheromones in addition to body-language and vocal tone. The Azdhagi use body language because they don’t have facial expressions. An Azdhag who can speak without any other bit of him or her moving is a noble, or is trying to be one, and is probably very dangerous if crossed.
*A semi-archaic American English term for money.