These days when we all are short of time and patience, the importance of a hook lies in the first line, and here are how some writers have done it:
"Nathan Rubin died because he got brave." Lee Child Die Trying.
"I must begin with a coincidence which I would not dare to recount if this were a work of fiction." Mary Stewart Stormy Petrel.
"What I felt as I got off the train this afternoon wasn't what I'd expected to feel." Robert Goddard Play to the End.
"The teenage boy was dying alone." Frederick Forsyth The Cobra.
"He gripped the steering wheel loosely as the car, its lights out, drifted to a stop." David Baldacci Absolute Power.
"To say that I met Nicholas Brisbane over my husband's dead body is not entirely accurate." Deanna Raybourn The Lady Julia Grey series, Silent in the Grave.
"By the age of twelve, Harry Valentine possessed two bits of knowledge that made him rather unlike other boys of his class in England of the early nineteenth century." Julia Quinn It Happens in London.
These all work because the author has asked at least one question we wish to find the answer to. While expanding on the first line, the first paragraph should raise more questions. The characters motivations. (What?) The story's time and place (When) and the reason behind it. (Why?)
The more questions you can pose in that first line, and the first paragraph, the better.
A great first paragraph by Lee Child Killing Floor:
I was arrested in Eno's diner. At twelve o'clock. I was eating eggs and drinking coffee. A late breakfast, not lunch, I was wet and tired after a long walk in heavy rain. All the way from the highway to the edge of town.
He continues on in this vein for some time, and we read it to find out why he was arrested. By the time we find the answer, we have invested something in the character and his problem. We are solidly hooked.
Nicci French. Catch Me When I Fall.
"I died twice. The first time, I wanted to die, I thought of death as a the place where the pain would stop, where the fear would finally cease."
In my romantic suspense, Casey's Luck I've used the weather to highlight the fact that not all is as it should be. I continue to ask questions. Some aren't answered until the end of the first chapter, some not until the end of the book.
"Why did the house feel so cold? Casey leaned on her elbows back into the narrow bed as the memory of the past few weeks ran through her mind, tightening her stomach. She'd hoped to escape the trauma of a broken relationship by returning to England, but the break-up seemed to have taken a piece of her she wasn't sure she'd get back."