Writers are often told we need to know everything about everyone in our story. Their childhood pasts. What they had for breakfast last week. The traumatic incident behind their deep-seated road rage. Their stance (or lack thereof) on the finer points of healthcare legislation. And not only people. We need to know how many construction workers died to build the 1930s-era skyscraper, with bonus points if any saw this as their chance to finally get back on their feet in the midst of the Great Depression.
This is especially prevalent in epic sci-fi/fantasy. An overgrown forest can't be just a forest. It is the forest where Shrum-Na-Fek, lowborn king of the sentient velociraptors, sacrificed his virgin bride to the dark god Ol-Ma-Shek, unwittingly cursing his people and opening a way for what are now called the darkwraiths to enter this world. Even today, people occasionally find a fossilized tooth of no animal that currently walks the land, and those who sleep with it under their pillows at night report strange dreams. If they're truly unlucky, the primal cries of madness haunt them evermore.
But even that's not enough. After the fall of the velociraptor nations, the sun turned red and bloated due to the war in space between the gods of old and the highly advanced space travellers from another galaxy who would take their place. As aurorae and falling stars burned the daylight sky, the forest shrunk to less than 1/5 of its ancient size.
But wait! It was this very catastrophe which awoke the Great Earth Goddess Squeeana, who in her attempt to remake the world after the War in the Heavens created the misshapen Thrith-Na, whose descendants plague the children of men to this very day.
But even they lay forgotten, dormant as the Middle Kingdoms fought their petty wars, some in this very forest, and the ghosts of the slain...
You might be able to get away with this if you're HP Lovecraft, but if not, and you throw all that backstory in at once, the infodump assassin strikes again.
The human mind is always stitching pieces together into a coherent whole. When it doesn't have all the information it needs, it just fills in the empty spaces with whatever it has lying around. Applied to writing, this means you only need about 3-4 descriptive tidbits for readers to get a good sense of what's being described. You can do more, but it can be an almost unavoidable temptation to drop everything in at once. For the finished product, it's not how much detail you have. It's what details you choose.
There are a few basic things which salient detail can (and should) accomplish:
Direct description: giving the reader a good sense of what's going on.
Creating atmosphere: giving the reader a sense of the overall environment/tone.
Foreshadowing: giving clues about the backstory which are later revealed.
Ideally, every description does at least double duty, but it can help to break things down into simpler elements for discussion's sake.
Tell the reader what something is, and trust them to fill in the gaps. Using the velociraptor cursed forest, this might be:
The forest a day's travel from town was ancient. As far as anyone was concerned, it had always been there. Some parts were so overgrown that even a man with a machete would make but slow and frustrating progress.
There are no hints of the forest's rich and illustrious history, but readers get enough of an idea to start visualizing the scene. Plus, there are only 3 distinct pieces of information: the forest is a day from town, it's ancient, and parts of it are extremely overgrown. For unimportant characters and locales, many times that's all you need.
Now to be a little more artsy, and create a foreboding mood around the forest. You might do it like this:
Some, especially the merchant guards whose caravans passed through it after dark, swore the shadows of the forest extended past its edges. While that was generally considered the idle talk of soldiers, the unspoken rule among local woodcutters was never to touch the old and twisted trees that lurked in odd clearings.
The reactions of characters in the story are a great way to do this, but again, don't go overboard. It's easy to get lost in secondary concerns, and the pace of the story will suffer. It's also possible to do this using analogies and words that have strong connotations or imply agency:
The waiting leaves at the forest's edge rustled in the breeze. Further in, the boughs of the synnis trees, taut as soldiers at attention, bore their pale blue fruit with an affronted dignity.
If you're looking to increase the difficulty, you can create the atmosphere appropriate to the POV character of that section of the narrative. The above description would be most appropriate to someone who doesn't like the forest. For someone who loves the forest, the description might read instead:
The green leaves at the forest's edge waved in the breeze. Further in, the boughs of the synnis trees, taut with anticipation, bore their light blue fruit like foodservants concealing their excitement out of propriety.
People perceive things different based on their mental and emotional states, and the exact same scene can be described very differently.
You can also drop details which hint at revelations yet to be revealed:
Occasionally the not-yet-apprenticed young men would venture into the forest on a dare or to impress a young lady, and come back with stone teeth. The superstition of old wives held that to do anything but bury them with a pouch of salt would bring the direst of misfortunes upon them all, but the more dashing and rebellious had taken to making necklaces of them. Those fetched a high price from the passing merchants.
Later, when dino-themed madness strikes a major metropolitan area, there were clues all along.
Details by themselves can become stale and uninteresting. It's the details that matter which breathe life into a story. Everyone approaches it differently, and like everything else this takes practice and self-reflection to get proficient.
Pruning the Weeds
- Pick a character or setting you know well. Don't use existing fictional characters; they've already been developed too much to be useful for exercises like this.
- List at least 15 important and interesting details that deserve to make it into a story.
- Write a descriptive passage using only four of those.
- Show the descriptive passage, but not the initial list, to other writers. See if they feel like they get a good sense of what's being described without knowing the history.
- Do this about 20 times, ten for people and ten for settings.
- Pick a place that you know well and love. Describe it in a paragraph, bringing out what you love.
- Pick a place that you know well and detest. Describe it in a paragraph, bringing out what you detest.
- Read over each of these paragraphs, taking note of the strategies (alliteration, analogy, descriptions, etc.) you used to evoke your feelings.
- Now describe the place you love as if you detest it, and the place you detest as if you love it. If that's a little too hard because of your emotional attachment, pick a neutral place, and describe it from the point of view of someone who loves it and then from the point of view of someone who detests it.
- Show your paragraphs to other writers and see if they can feel the emotion.
- Do this a bajillion times.
- Create a character with a dark and troubled past, one which will bite them in ass eventually.
- Write a paragraph describing that character, hinting at the past but not revealing it. "He looked as though he has a dark and trouble past" won't cut it. Try to be more subtle and specific, along the lines of "Despite his impressive musculature, he always favored his left side when walking, and even a quick jog would leave him gasping for breath" for a time-travelling space marine whose last jump went awry, tearing up his insides and stranding him in the 21st century.
- Show your paragraph to other writers to see if they feel like the description isn't too blatant.
- Then, tell them the character's backstory and see if they feel like, now that they know, the description fits.
- Repeat until second nature.