I've seen writers make one of two mistakes when setting the scene: not writing enough or writing too much.
How much do you need to tell them?It depends on the importance of the setting. In some stories, the setting is so vivid it becomes a character in the story. In other cases, we just need to visualize where we are and what's happening. It doesn't all have to occur in the first sentence, you can filter in details as the scene progresses as long as you give the reader some idea of the setting.
For example, this is the opening scene in a short story I wrote that received several awards including a Pushcart Prize nomination:
The minutes ticked by in agonizing eons, drop by drop in time with the saving liquid in the IV bag hung by Bethany’s bed in the ICU. Jane, her mother, stared at the fluid wondering how it helped, if it helped, her daughter. The young girl lay on the bed, still and quiet as death, her skin paler than the white sheets hiding most of her injuries.
In three sentences, I've set the scene. We know we're in an ICU unit in a hospital, so we don't need a lot of information to give us that visual. Most people have either been in a hospital room or seen one on TV. Notice, these sentences do more than provide the setting, though. We know Jane is Bethany's mother, Bethany is young and injured, and Jane has been by her bedside for a long time.
What if the scene is not something the reader can readily pull from their memory? Here's the first paragraph of Chapter 1 in one of my fantasy novels:
Adana believed deep within her soul that her actions today could save her mother. The air around her crackled with heat from the unrelenting sun, as she stared across the archery field at the target in the distance. Sweat trickled down her back. No air stirred, but she could smell the pungent incense burning in the estate’s halls. Death clung to the air she breathed, unwilling to relinquish its hold on the kingdom of Moniah and its ruler, her mother.
Moniah is a fictional place as in most settings in fantasy. In this chapter, we know it's hot and dry. We realize we are outside in an archery field at an estate for the ruler of Moniah. As the story progresses, I drip in pieces of information to help the reader visualize and experience the setting. When you create the setting from scratch, called world-building, you can't dump the whole description on the reader at once. They will lose interest. Give them what they need when they need it.
Once again, these first few sentences provide more than the setting of the story. We learn that Adana's mother, the ruler of this kingdom, is ill and probably dying; Adana feels a responsibility to change the outcome of her mother's illness; and this culture burns a pungent incense during illness. The last sentence hints at the idea that others might be ill, too.
How do I check for setting?Take a look at the first few paragraphs of any scene in your manuscript. Did you show the reader the setting or leave it to their imagination? Each scene needs some description sprinkled in with the narrative of what's happening.
Setting carries a lot of weight in a story. If you're still unsure how to set your scenes, ask yourself this:
What book, for you, gave the most vivid setting of the story? How did the author achieve it?