We all know that a good setting for a story is important. I love to build worlds, and I know many people who visit here do, too. Sometimes very extensive ones. Of course, that doesn't mean that mainstream writers don't have to work on their worldbuilding too - they're just building a version of the real world instead of an independent, alternate world.
When we talk about setting, we talk about all kinds of elements that a world has - climate, ecology, flora, fauna, human/sentient communities, demographics, economy, social structure, technology, etc, etc. Everything we think through in our worldbuilding process can be useful to the portrayal of a world in a vibrant way in a story.
Super. But setting on its own isn't enough to make a story take off - every story needs grounding.
This might best be explained with a metaphor.
As a writer, you want to take your reader on a journey. You want to grab them by the hand (or the hair, the shoulder, or the guts, depending on the kind of story) and pull them through the story with you. If you're like me and you want to create a really exciting hook, that means you want to grab them as quickly as possible and start pulling with as much force as you can. Grounding, then, is the difference between having them running alongside you and having them pulled to their deaths behind galloping horses. If you want the reader to come with you - especially at a very quick pace - you want to start by giving them a solid place to jump off from.
On a basic level, grounding is about who/when/where. Who am I (the narrator or protagonist)? Where am I (the physical location)? When am I (the chronological location)? Each of these things can be indicated or elaborated in different ways. The reader isn't looking for every detail of your worldbuilding here - only some basic orientation that can be provided by a personal pronoun (I, he, she) and a sense of voice (who), a description of light or of nearby objects (where/when).
You'll probably tell me at this point that not every story needs all this. What about stories where the narrator is disoriented, lost, disembodied, or otherwise compromised, and doesn't know where he is? What about the confused time traveler?
Well, you're right. The type of grounding required by a story depends on the story. If you're going to have a physical departure from a location, you need a sense (even a confused, internal guess) of what that location is. A pitch-dark place with a hard floor can be enough if properly conveyed. If you're going to have personal interactions, it's good to have a sense of who the narrator is.
Look at your story. Pay particular attention to the place where the conflict starts - the spot where the hook grabs and pulls in a direction. The nature and direction of that pull will tell you what information might be needed for grounding.
Let me give some examples from my recent experience.
I was reading a draft from one of my many writer friends recently, and felt confused. I thought the protagonist was standing in one place when she was standing in another. I looked back at the descriptions, and the sentence was clear: a different character was standing in the spot where I'd mentally put the protagonist. There was no ambiguity. But when I looked back over the previous paragraphs, they were all internalization - excellent grounding for the mental and moral position of the protagonist, but not of a physical position. Because the different character was located physically, I needed to ask my friend to give the protagonist a physical location as well.
When I was drafting my story, "At Cross Purposes," I discovered that first-round readers were confused at the start. Yes, I was trying for a very quick hook. I was also creating a story where two unexpected things happened one right after the other, and I didn't have enough information to have the two departures make sense as departures. I needed to go back and establish physical location (she's on a shuttle!) and ongoing activity (they're flying around servicing machines) in order for those departures to be more tolerable to the human brain (she discovers something that shocks her, and then it turns out not to be at all what she expected). If you think about it, a departure from expectations means little if you don't have any sense of what expectations are.
I'm currently working on a story with a narrator who is supposed to start as an enigma. Reading about him, you're supposed to wonder, "Who is this guy, precisely?" What you're not supposed to wonder is "What the heck is going on?" I was quite happy with my first sentence, which was, "Of course people write letters; I knew that from watching the monks." The grounding here is that we have a character (I) who watches monks, which implies he's at or near a place where monks live. The next hint as to setting was that the character expresses dislike of letters written in Chinese, because he doesn't care about court business - that at least lets us know we're dealing with Asian monks rather than European ones. Then someone writes the narrator a letter, and the letter is composed in a very particular style that is specific to an era of Japanese history. The problem was, the hints were too sparse and too indirect. I needed better location and time grounding if I wanted readers to accept the style in which the letter was written. So I added the name of the temple, Ninnaji. That gives readers a Japanese language hint, and then optional for those who know about temples and Japanese history, is the fact that Ninnaji is an existing temple in Kyoto which has been around since the Heian era. Then I added that my narrator had stolen the letter in Chinese from "the Emperor's messenger." While that's not specific to the Heian era, it at least is an indication that the time period isn't the present day, and I'm hoping it will get readers looking for further clues - in which case, the letter-writing style can be a clue rather than a mystery.
No matter what the setting, every story needs grounding, and the choice of grounding information is critical to the success of a story opening - so keep your eyes out for it.