Scholastic suggests grabbing a reader's attention by opening with a surprising fact or anecdote. Unusual information can jar your reader and gain his attention -- even if he doesn't believe the fact you're sharing. For example, you might begin your story with a monologue by a main character. Within the monologue, the character might present a surprising scientific tidbit or a strange personal story about the past.
People are emotional creatures, and an emotional hook can quickly draw your readers' attention. You might try starting with a character's internal monologue about intimate feelings, or show a scene that demands an emotional reaction -- such as one involving domestic violence, war, a fight between a parent and child, or another common or emotional human experience. Lincoln High School's Writing Center points out that the way emotional language is worded matters, using the example of "Fahrenheit 451." Rather than beginning the story by stating that books are being burned, Ray Bradbury opens with the emotionally charged line, "It was a pleasure to burn."
Your readers are reading your story because, ultimately, they want to know what happens. Fiction writer Laura Backes argues on "Absolute Write" that many good hooks create tension by raising the stakes for the characters. You might open your story with a serious dilemma that a main character has a limited time to solve. A woman might only have five minutes to get home and catch her husband cheating, or a child might be racing away from bullies on his bicycle.
Writer Tiffany Lawson Inman of Rocky Mountain Fiction Writers points out that the wrong approach can destroy an otherwise good hook. Avoid giving readers too much description or back story. This may bore or confuse them. The goal of a good hook is to help your reader become interested in your story, so limit your hook to the most interesting and compelling information.