The past-midnight quiet in Yuelianq Thief-Keep came to a sudden end when a knife came flashing out of the dark. The knife buried itself point-first in the wooden crescent of stool showing between the night-jailer's legs.

Stephen L. Burns, Taking Heart

Got your attention?  That's because this writer has opened with the first classic way to grab the reader by the throat -- with action.  In fact he's combined action with some of the other tricks of the trade I'm about to list, but let's look at some other examples for those.

Trick number 2: pique curiosity.

I smelled her before I saw her.

Spider Robinson, God is an Iron

Who is "she"? Why does she smell? Does she smell pleasant or unpleasant? What will the speaker--and the reader--"see" when he sees her?

Trick number 3: succinct and striking characterization.

You could say this of Harvey Hennicutt -- he was an exceptional liar.

Rod Serling, The Whole Truth

Serling in particular is a master of focussing in on characters we know we want to keep watching.

Trick number 4: hint at dramatic tension to come.

When the phone rang, Dave Potter seized it with a desperate relief he tried not to let Caroline see. From the way her face froze and she turned her back away from him and toward the sink full of dirty dishes, Potter knew he had failed.

Nancy Kress, Phone Repairs

Whatever this phone call is about, we know there is already some underlying disagreement between the couple. We know something is going to happen between them.

Trick number 5: Horrific or arresting language or imagery.

Un and Sub, the giants, are grinding him for bread. Broken pieces float up through the wine of sleep. Vast treadings crush abysmal grapes for the incubus sacrament.

Philip Jose Farmer, Riders of the Purple Wage

Horror fans love a horrific image, but just gore will bore. Originality lets you know this story won't be like any other.

Trick number 6: Overthrow normal expectations.

Once upon a time, in the small town of Smunsk, during the reign of Cinnabar the Second, a baby was born into the Guild of Seers, Speakers, Dreamers, Storytellers and Non-Fanatical Prophets.

Michael Rutherford, The Tale and its Master

This sounds like a typical high fantasy, told in traditional style-- until we reach "Non-Fanatical Prophets", and realize the author has tongue firmly in cheek. We keep reading to see what else of an unexpected nature will turn up.

SF, Fantasy and Horror are much more dependent on setting and atmosphere than mainstream fiction, so it is sometimes tempting for genre writers to thoroughly "set the scene" before getting the story moving. Readers (especially editors and agents) may forgive this in an epic-length novel by an established author they know will deliver the goods, but even Stephen King knows not to presume too much on the patience of his readers.

For want of a nail the kingdom was lost -- that's how the catechism goes when you boil it down. In the end, you can boil everything down to something similar -- or so Roberta Anderson thought much later on. It's either all an accident... or all fate. Anderson literally stumbled over her destiny in the small town of Haven, Maine, on June 21, 1988. That stumble was the root of the matter; all the rest was nothing but history.

The opening paragraph of the mammoth novel The Tommyknockers, above, piques curiosity with "...or so Roberta Anderson thought much later on..." and provides action in "...literally stumbled over her destiny." We know it's only a figurative kingdom and figurative nail to be lost in this story--though already by the end of the first sentence we want to know what figurative kingdom and nail--but then to find it's a literal stumble the protagonist makes--that's reversing expectations as well as action.

The rule of thumb for grabbing a reader by the throat is: the shorter the story, the sooner you'd better do it. Otherwise, dear writer, they're going to put your story down and go read Stephen King, Rod Serling or Stephen Burns.