It is, of course, so named because you want to hook readers at the very beginning of your story. The point of the first sentence is to get them to read your second. We want them to continue until the reader walks out of the bookstore with our book or clicks the buy button online.
Opening lines can be flashy or subtle. These are some of my favorites.
“If I had cared to live, I would have died.” John Myers Myers, Silverlock.
“Sam Vimes sighed when he heard the scream, but he finished shaving before he did anything about it.” Terry Pratchett, Night Watch.
“This time, there would be no witnesses.” Douglas Adams, Dirk Gently’s Holistic Detective Agency.
“When I wake up, the other side of the bed is cold.” Suzanne Collins, The Hunger Games.
What do all of these have in common? They get the reader to ask a question. This can be a fine line to walk. You don’t want them to ask too big a question and get knocked out of your story. But the reader needs to be curious enough about your opening sentence to read on.
In addition to this, though, I’ll add the caution that an opening phrase makes a promise to a reader.
“John smiled as he pulled the trigger,” could be a worthy start. But if this is the only violent action in the book, and the rest of it is spent on how John’s encyclopedic knowledge of stamp-collecting saves the day, you’ve made a promise to the reader that you didn’t keep.
Also, the opening sequence must be important to the story. Using my above example, if John was a police officer, that line would be appropriate for the type of story you want to tell. But if it’s part of a narrative of the first time John ever fired a gun, and this has no bearing on your particular thriller/mystery, you’ve lied to the reader about the story that follows. Using character development as a reason only goes so far. The scene should matter to your plot, no matter where it is.
That’s not to say you can’t open with an action sequence to pique the reader’s interest. Many successful books and movies do. By doing so, they’re promising the reader, “Yes, my protagonist is really a person of action. They may be floundering early on. But don’t worry, (s)he’ll move the story forward, not be carried by it.” And that’s a good thing, if you keep the promise.
Another caution I’d add, unless the first line of your story is a prologue that you must keep, is that the first line should stay close to your protagonist, unless there’s a good reason for it to do otherwise. Get us invested in your main character, in their point-of-view, unless you have a compelling reason to begin with another character, like the antagonist.
Many agents (and readers) don’t like a story to start with profanity, graphic violence, or explicit sex. Shooting a gun is okay. Picking up a child and bashing her brains out—not.
Clichés are usually a mistake on an opener. If you have any doubt, rephrase.
Similarly, avoid overused characters. Blonde bombshells, hard-boiled detectives, criminal masterminds—these have all been done so much that the result is likely to be a bored reader. Don’t introduce a character nobody will care about.
Start off with showing us snippets of your world—don’t tell us about it. And really don’t begin your story with a long, dry, telling exposition, also known as an infodump. It doesn’t matter if you think your readers need this information to enjoy the story. If that’s really the case, write a different story. Most writers, when faced with this ultimatum, can suddenly think of ways to do without that prologue of How Their World Came to Be.
And don’t worry if you can’t think of a hook as you write your first draft. Start writing your story anyway. Many first chapters are rewritten after the book is finished.
Your opening sentences are your chance to impress potential readers enough that they will part with their hard-earned cash to read your words. Don’t squander them.