One of the difficult elements (are there any easy ones?)  in openings is how to sow information into the seedbed of the story in the right amounts and with the correct distribution so that

1)  the reader will not get bogged down in a rain of information such that they put the book down

BUT

2) the reader has enough information to orient them-self in the story

AND

3) the information sown over the early pages can sprout in a timely manner later down the road so as to enhance the narrative experience.

The flip side of information distribution in openings (and throughout a narrative) is that with too little information the reader becomes lost, or the story starts shallow and keeps wading.  Furthermore, without proper distribution of the correct (most significant) information, the writer may have to explain the impact of certain big plot points or dramatic emotional moments when they happen rather than having the impact hit the reader because of what the reader already knows which the writer has cleverly seeded into the story.

One of the surest ways to bog me down, as a reader, is to pause the narrative flow to back-fill information the author is sure I need in order to understand the context or empathize with the main character(s).  Because I often don’t NEED to know that information yet (or in some cases ever, especially not as an infodump), and I really don’t WANT that information interrupting the flow of the story.

How much and what kind of information the reader needs will vary depending on the narrative.

In genre it may also depend on whether this particular book is one of a sequence or series in which the reader may need, or be expected to have absorbed, context from an earlier book or books.

I’m going to stick with what I know, which is genre.  So these are not hard and fast rules (I’m not one for hard and fast rules anyway), and they are particular to the genre I am most familiar with. But as a general template in terms of how I try to write and how I read, they’ll do.

When deciding how much and what information to seed into your opening, take into account:

what does the reader NEED to know vs. what you think the reader needs to know

what does the reader WANT to know vs what you want the reader to know

Often what the writer thinks the reader needs and/or wants to know is in fact more than the reader needs and/or wants to know at that stage in the game.  Sometimes it is less.

I personally have a lot of trouble with stories in which I’m given too little information to place myself in a landscape, by which I mean a physical and a cultural and a historical landscape. However that statement definitely reflects my own personal tastes and will not be the same for all readers, because I guarantee that one complaint I hear about my own novels is that there is too much information ladled down the reader’s throat too early.  So be aware that, as a writer, I am constantly struggling with this myself.

For it is remarkable, really, how little we need to know as long as we have exactly the right information to hook us into the story one way or another.

If we feel grounded, and are interested in finding out more, curiosity and engagement are part of what pull us on through the story.

The reader usually (not always) needs to know

1) who is the character(s) I’m following

2) why, in the most immediate sense, I am rooting for or against that character (an emotional hook);  rooting for or against does not have to mean “liking” or “sympathy” although that may be the specific effect you are going for

3) where am I?
3a) secondarily to “where am I” – why does it matter that I am HERE rather than in some other place.

I don’t mean that last sentence literally but figuratively, perhaps even culturally.  While there are circumstances in which a character must literally reflect on why it matters to him/her personally that s/he is splayed on the altar about to be sacrificed to the demonic hordes, more often this is an embedded quality inherent to the story.

Why HERE matters in the immediacy of the plot is not because you are explaining it to the reader but because it is accustoming the reader to a landscape which should matter in the larger scheme of things as the story continues.  Because it should matter where you are and why you are there as opposed to someplace else.  If your story could start some other place, then why isn’t it?  Using an unthought-through default will flatten your affect and present both a weaker opening and a weaker story overall.

This ties into the idea that what the reader must know intersects most commonly with points later in the story where the plot must turn, change direction or focus, or alter speed.

An opening generally includes focus on the part of the reader, and an element of turning inward and altering speed to match with the pace of the developing narrative.  That’s why the balance between information, action, and character needs to be so precise.

There are a number of ways to approach the deploying of information

1) set a simple scene, that is, a basic picture in the mind
    Joan stood on a hill overlooking the ocean.

2) reminders of backstory
In the context of a standalone or first novel, I call this backstory.  In the context of a subsequent volume of a series or sequence, I call this backfill. (These are just my personal terms; you don’t have to agree with or use them.)
These can be accomplished

within character interaction:
“Hey, Joan, how’s it going?  You get all that werewolf splatter from last night cleaned off your windshield?”

as reactions:
Joan looked up from trying to wrestle her key into the car door to see a big black dog running across the parking lot toward her.  With a shriek, she bolted over the asphalt, dodging the last few parked cars, and ran back into the store.
(This is backstory because her actions tell us of what happened just before the dog appeared.)

as reflection:
Never again would she look at dogs in the same way.

preferably not as infodump:
Joan stood on a hill overlooking the ocean.  Last night had been the worst one in her life.  She was a clerk at an office store, and when she had left the store at closing she had walked out to her car still irritated with her boss, Joe, who despite being a good looking single guy was so cheap that he hadn’t yet replaced the lights in the burned out fixtures in the parking lot.  Her key had gotten stuck in the lock again when she had heard a low whine and the clicking footsteps of an animal running toward her across the asphalt.

3) set up
Joan stumbled over the crowbar Jake had carelessly left on the grass in the front yard.  Damn it!  She checked her watch. Late already! She tossed the crowbar in the back seat of the car and then drove to work.

For some stories it works to use as many elements as possible.  The more you can combine character, plot, backgrounding, conflict, and impetus, the more punch you will get from the information you do disclose.  In such cases the key is to streamline and highlight the information  in a way that does not confuse or overload.

Other stories take a much simpler approach, relying on some element of familiarity–a familiar setting or motivation or setup–to engage the reader’s understanding of where and what and then letting the hook be the twist or spark that leaps out as unfamiliar or captivating. That is, you build on an existing model that you, the writer, think the reader will be familiar with, say “the new kid’s first day at school” or “arriving at the gates at sundown just as the guards are locking up for the night.”

As always, with information, you the writer have to decide how much to reveal, how much to hint at, and how much to save for later.  Balance is everything.