When beginning his next novel, Stephen King will spend weeks, if not months, on perfecting the story’s opening sentence. He does this to find that particular invitation readers will find too tempting to pass up. When he has that perfect opening sentence, the rest of the story flows.
To craft that opening line, which establishes character and setting, you need to have something that hooks the reader. To do that, you need to find the right words to unlock the idea you’ve been haunted by into something larger.
Speaking of haunted – here’s an example of a gripping opening line by the incomparable Shirley Jackson:
No live organism can continue for long to exist sanely under conditions of absolute reality; even larks and katydids are supposed, by some, to dream. 
Immediately following that sentence is the introduction of Hill House, reputedly haunted, not lived in and still kept in pristine order by a couple from the local village. Each sentence builds on the next and you are drawn into the lives of four people, determined to prove that Hill House is haunted. Although it averages two hundred or so pages, it is tightly constructed, spare and ambiguous, leaving you wondering – is Hill House haunted or is it all a figment of Eleanor’s mind?
And neatly tying it all together, the final sentence of the novel echoes the final sentence of the opening paragraph – and whatever walked there, walked alone.
 The Haunting of Hill House (1959)
(The annotation below is brilliant.)