: How do you drop a reader in the middle of nowhere at the beginning of a story? My story begins with a little girl waking up in a creepy and probably very haunted house in the middle of

how should I start the story?
This is obviously a matter of opinion, the story I would write may be far different than the story you want to write. So this is basically how I would start such a story. (All elements can be toned down for a non-adult story.)
You need to establish the little girl as your hero, which means she has to be able to overcome her fear and DO things. DOING is very important for character likability, rely less on pity (because she is a frightened little girl) and far more on a natural inclination to try something even if it fails. Think of Bruce Willis in Die Hard; a long series of failures, getting beaten, cut, bloody, burned, always just barely on the trail, he's like Wile E. Cayote vs. The Roadrunner, except he prevails in the end.
So she may be fearful when she wakes up, but she does NOT deal with fear by taking the fetal position under the covers and waiting for a ghost to force her out of it. She does not try to hide in the closet. She deals with fear by taking action; searching for her mother or father, or whatever is the last thing she remembered. If her door is closed, she will open it. If it is locked, she will try to force it. If she can't, she will try the window. If that doesn't work, she will break it with the lamp.
Her fear cannot be disabling (or never for long), it must be accompanied by determination to move forward, to open the next door even as her hand trembles in fear, she doesn't back down. It can help her likability if she has to hurt herself: Jump from a height; grab something on fire; intentionally cut herself for the blood it takes to open a magic book.
Start with her taking action, what she does will define her character, and that will lead you to the rest of the story. Her reaction will be to find out where she is, and if confined, to escape.
You start by her asserting those goals (through action) and failing to achieve them: She cannot figure out where she is (nobody answers her calls), and she cannot escape (leave the room). That first scene can be a microcosm of what the story is about: She needs to escape the house, but first she needs to escape the room.

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Is it a bad way to start the story?

It isn't. In fact, it can do what you want to do in the first place: hook the reader. Writing in the middle of some action or plot gives the air of mystery which readers would then be interested in finding the reasons for. Your next job is to address this.

How should I start this story? What should I focus on?

Well, key things here are the basic questions your readers would ask:

Where/When are we? : You'd like to set the mood, picture the landscape but not excessively. You'd want to keep the reader in the dark just enough to keep pulling him into the plot. Depending on the genre of the story, I'd go for sensations (tactile, visual, etc), build the tension and keep it there.

Then address what your character would ask:

Why am I here? : While this wouldn't normally be answered immediately, you'd go ahead and drive the protag forward with this in mind. What are her initial thoughts on the situation? Does she feel nervous or calm?

You should focus on the matter at hand basically, the character is plunged into a world she doesn't know and exploring it would be the only option. Her reactions would be the brush to paint her personality and the world would be further expanded by how she views it.

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In Media Res

Your idea of starting right in the middle is a good one and is used by the best stories. Readers quickly become bored with stories which just tell a lot of backstory.

The idea is such a great one it is an actual literary term known as In Media Res (https://en.wikipedia.org/wiki/In_medias_res) which means "into the middle of things".

That's what we want to do as writers, throw our characters (and readers, vicariously) into the middle of the action.

Your next question was:

What should I focus on the most...?

That is easy and difficult to answer.

Easy Answer

The easy answer is focus on what is important to your story. Focus on what the character sees and experiences.
That leads us inexorably to the (more) difficult answer.

(More) Difficult Answer

The difficult answer isn't really more difficult. It actually makes logical sense too. However, it is more work.

Act Out The Scene

The way to get to "what you should focus on" is to act out the scene in your head.

Ask Yourself The Following Questions

How would you feel, if you awoke in a strange place?
What would be the first thing that would go through your mind? (Where am I? Where was I last?)
While you are thinking those things, how would your body react? (Cry? Curl into little ball?, etc)
What actions would you then take? (try to find a way out?, cry more?)

Visualize The Scene

Begin to visualize the actual scene taking place with yourself as the protagonist. Capture the reactions step by step in your writing and write it clearly so someone else can see the scene play out in front of them.

If you follow these simple steps you will find that your fiction becomes very realistic and will be clear for readers.

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Some of my favorite books have started in essentially this way, with a protagonist who doesn't know who he or she is, not to mention where or why -- these include Raw Shark Texts, Nine Princes in Amber and Dhalgren. For me, I think it works because it's often the experience we have in dreams, or occasionally in the first minutes after waking up. There's a burst of energy from the setup of trying to solve a mystery without even the most basic information. So this is a solid idea for a start to a book.

The bigger challenge, however, is making sure the book pays off on the setup. Is it going somewhere that makes it all worthwhile? Each of the books I mentioned above pays off its premise in a different way. Raw Shark Texts gradually explains and justifies its mystery, the Amber series solves its initial mystery quickly, but opens new ones as fast as it solves the last one, and Dhalgren is ultimately about going on in the face of the insoluble mysteries of life.

Just remember (to borrow a concept from Mark Baker), your opening pages of your book create a contract with the reader, a set of implicit and occasionally explicit promises about what the book will hold. It's your job as the writer to fulfill those promises by the end, if you want readers to go away satisfied. A beginning is nothing without an ending.

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This is a somewhat usual start for something that goes in the direction of a horror story - which means it works for the general audience
You will want your character to wake up and have a look at her surroundings. After getting a first impression you should dwell for a moment on the fact that she does know who she is, but she does not know how she got to this place and why she is there - there is a gap in her memories.
Often you will find that this gap is an important part in keeping the reader engaged by giving them little bits of information and having the character remember a bit more. Maybe they only remember leaving their house in the morning like every other day - before suddenly waking up in this cold and dark place, their head hurting like they've hit the ground pretty hard. And then they slowly start to remember how they took the bus after leaving for work. For example because they met a friend there and something they found in the creepy place reminded them of that friend.
It's a normal way to start and like every story has been done quite often. That means it works pretty well and as long as your character is engaging and your narration of the environment is interesting your readers will probably like it - they likely expect something in this direction from a horror story.
You need to keep in mind:

Who is your character? -> What does your character know? What do other characters that are nearby know?
What is the last thing your character remembers? -> What are important bits that need to be recovered? What are helpful things that your character will try to act on?
Where is your character? -> What does it look like? What does it smell like?
How does your character feel in this situation? -> Is your character scared out of their mind? Is your character trying to remain calm as best as possible?
What will your character first try to do? -> Will your character run away at the first noise from a mouse? Will your character try to examine the room they woke up in?

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