Here are examples from two of my books:
"Nate Cancaid sat straight up in bed, gasping like a drowning man who had finally reached the surface, each breath wrenched from his chest." ~ Dream Man, romantic suspense.
"I'm in big trouble." ~ The Bettin' Kind, Avalon Books, sweet historical.
The opening sentence should make the reader ask the question-why? It should draw their curiosity and make them want to read the next sentence. It should also relate to the overall story question.
In Dream Man, Nate must figure out the connection between his reoccurring dream and a thirty-year-old missing persons cold case.
In The Bettin' Kind, Amelia Morgan sacrifices her dowry and herself to save her little brother.
Hooks are not only found in the opening of a book. Each scene, each chapter should end with a hook. Why? Because you don't want your reader to put the book down. You want them to feel the need to turn the page and find out more. If you get really good at this, you'll have your readers up all night reading. They might curse you for it, but they love it. And you've done your job.
Look at the books you've selected. Thumb through to the last sentences in the first chapter. Write them down. Does it make you ask a question? Does it get your curiosity up? Do you need to take a sneak peak at the next chapters opening hook?
Examples: "...Do you realize what you just said?" "I know what I said," She kept her voice low but firm. "I know what kind of danger saying it put me in, especially with Tom running for President. But let me just tell you one more thing...she asked for you by name." ~ Dream Man, chapter one end.
"She shut her mouth and glared at him. He knew in her heart she didn't believe he would do it. But, of course, she didn't know him. If she thought anything other than her own refusal would save her, she was dead wrong. The men in the barbershop came over, introducing themselves to Alex and slapping him on the back. They almost pushed Amelia away, but Alex wasn't having any of that. He didn't want her to get away. Not before he got his horse." ~ The Bettin' Kind, chapter one end.
As a writer it is your job to draw the reader in and keep them turning pages. Study your favorite authors' chapter beginnings and endings and you will discover a wide variety of ways hooks are created, but be careful, you might get drawn into reading the story. Cheers~