Sarah's offered quite a lot about remembering that there's someone on the other end of the book, and way to keep that person reading. I'm going to look at one specific part of that: the scene-setting and cuing in it offers.
How many times have you read something where the author switched track on you, and the book turned into something you weren't expecting when you started it? And how often has it irritated rather than delighted you? Yeah. I thought so. See, we're so attuned to what a story should be, we can pick up - subconsciously at least - what a story is about from very little.
Take for instance the opening to Pratchett's The Color of Magic - In a distant and secondhand set of dimensions, in an astral plane that was never meant to fly. That one sentence is enough to cue readers in to several things: we're not in Kansas anymore, and it's not going to be reality as normal. Oh, and it's almost for sure fantasy. Comic fantasy.
It might not register at the conscious level, but we're primed for laughter.
Of course, this is Pratchett, and even Pratchett of nearly thirty years ago stands head, shoulders and quite a bit more over every other author alive today (although in my not at all humble opinion both Dave and Sarah are climbing that particular mountain at speed).
So how do we lesser lights set the scene? There's a few things to consider.
First up, and possibly most important, each genre and subgenre has its own distinctive 'feel' and tropes. Standard practice in a cozy is utterly verboten in splatterpunk horror, and so forth. The mood we set has much the same effect as a movie soundtrack - more or less invisible (or it should be) but puts the reader's emotions where we want them. Yes, it's manipulative. We're playing with people's minds because they want us to. If they don't like us hitting their emotional buttons, they don't have to buy our books. Next question? Good.
Okay. I got bitten by this not long ago, in a crit group looking at the opening of my current work in progress. The piece is typically Kate-weird, meaning it doesn't quite fit into any nice, neat slots. It's more or less space opera, but it's also got elements of erotica, in that quite a bit of the plot is carried by and depends on sex. Specifically, somewhat kinky sexual practices that aren't so much as hinted at in the start of the book. The advice I got, not suprisingly, was that I need to have the sex up front so that it's not picked up by someone who reads the opening and thinks it's okay for young teens. Or, for that matter, so editor X doesn't start reading thinking "light-hearted space opera, a bit of a romp", get to the sex, and have his, her, or its brain explode.
Attractive as the notion of making peoples' heads explode might be, it's really not a good idea to do that to people you want to give you money, so... I need to put sex up front, preferably in a way that foreshadows the kind of sex that happens later on (especially since said sex is emphatically not garden variety vanilla). What I start with now says "lightweight space opera, with humor".
As to how you do it, it's all in the power of words. English has a phenomenal number of synonyms, most of them with very different emotional/atmospheric connotations. Let's take, for the sake of example, sex. We all know what's involved. Call it making love, and it becomes a much more intimate act. Or take desire, longing, yen, urge, obsession, need - they all mean more or less the same thing, but the flavor varies. A lounge, a sofa, a Chesterfield... Curtains, drapes. And I haven't even gotten out of the common words.
For science fiction, probably the most common trick is faux tech-ese and using technical terms instead of the normal "earthbound" words. Epic fantasy and sword and sorcery often go the other way, using archaic forms of common words - sparingly. Urban fantasy generally maintains a conversational, smartass tone and uses a lot of not-quite-slang, enough to make it sound cool (or whatever the designated word for that is these days) without being so cutting edge it dates the book between the time it's written and the time it's published (For an example that dates a book, read Hitchhiker's Guide to the Galaxy and then tell me you don't see late 70s written all over it). Horror of course pulls all the stops out: cognitive dissonance, bleak or grim descriptors, and every possible trick in the writer's vocabulary to make the whole thing bode. An excellent guide to the process is Stephen King's Danse Macabre, containing the famous quote about terror, horror, and gross-out. A good thumbnail distinction here is that terror is being in an iffy situation and realizing your buddy is missing. Horror is finding your buddy in a closet - and he's not alive. Gross-out is when the alien or monster comes out of his chest, usually featuring loving description of the effects. The word 'glistening' gets used a lot, even when there shouldn't be enough light for anything to glisten. As a general rule, if you're wanting to scare your readers, aim for terror. Drop to horror only if you can't manage terror. And gross-out is the last resort. (Yes, Stephen King said approximately that, and yes, he will go for the gross-out if he can't make terror or horror happen).
Let's have a few samples of story openings that do a good job of setting the scene. Short or long, yours or someone else's (if it's someone else's, please acknowledge the author). No more than a couple of lines - most of the good ones don't need more than that.
Here's one or two of mine, just to kick things off:
There are times when being a Quality Assurance Mage sucks. The silvery gray spell-ball on my desk told me today was one of them. Fantasy, rather whimsical, may or may not be urban. From my short story A Spell of Quality in Misspelled. This sale was an invitation, so I didn't need to have the higher standards that anything going through regular slush has to have.
The great looms stood silent, strands of Scylla-silk glimmering in semi-darkness above the completed weaves. Air heavy with the acrid tension of electrical discharge sparked and crackled with each of my cautious steps. Science fiction, fairly dark. The use of words like "heavy" and "silent" suggests that this isn't going to be a particularly fluffy piece (accurately, as it happens). This is the opening of my short story Choice of the Oracles in Fate Fantastic - another sale by invitation.
Another convention, another con hotel. After a while, they blur together into an indistinguishable mass of faux-elegance and bizarrely costumed fans. This is the opening of ConVent a novel which - alas - remains homeless. The setting is pretty obvious, and the tone suggests urban fantasy. Anyone who's ever seen photos of a busy science fiction convention can see the scene. So, for that matter can a heck of a lot of people who haven't been to one - because I've played on the stereotypes of science fiction fans with this opening.
What are some of your examples?