I am not a Stephen King fan but I seem to be quoting him a lot lately; he is brilliant on the craft of writing. There was a fascinating interview with him The Atlantic in which he explains why he spends 'months and even years' getting the opening sentences of his books right. For him, it's not just about hooking the reader in (though that's crucial) but about hitting on his narrator's voice. Very interesting.
A killer opening sentence is probably a key part of thrillers. Think of Brighton Rock by Graham Greene: 'Hale knew, before he had been in Brighton three hours, that they meant to murder him'. Brilliant. But I'm not sure if it's that crucial to chick lit/romantic comedies. Here's the opening sentence from Emily Giffin's Something Borrowed:
'I was in the fifth grade the first time I thought about turning thirty.'
That's intriguing, but I don't know that it would pass the Stephen King test. Here's Marian Keyes, Last Chance Saloon:
'At the chrome and glass Camden restaurant the skinny receptionist ran her purple nail down the book and muttered, 'Casey, Casey, where've you got to?'
Similarly, that's a relatively casual opening line to a brilliant story. But what both of these opening sections (as opposed to just opening lines) do is to dramatise, very cleverly, the main character's key dilemma. In Something Borrowed, we find out that the heroine Rachel's fifth-grade birthday falls on a Wednesday, a school night, and Darcy's birthday is on a Friday. 'A small victory, but typical'. And this sets up the rivalry that will run throughout their very long friendship. In Last Chance Saloon, Katherine is the first to arrive to meet her friends despite forcing herself, 'every fibre in her body resisting', to be five minutes late. It's crystal clear; her life is too controlled (while her friends are all over the shop).
Openings are really, really hard; the opening chapters to both of my books went through about 20 revisions before I found the right scene to dramatise the heroine's central problem or dilemma. In If I Could Turn Back Time at one point I had Zoe calling the Samaritans in tears because she was so upset over David … it was meant to be funny but it was a bit of a downer, so it got scrapped. Mostly, the openings are the last things I perfect. So I would tend to advocate NOT spending months/years crafting the exactly right opening sentence before you continue. Just bash your way through and you can come back and fix it later. This advice is just one of the many reasons why I'm not Stephen King, but, you know, different strokes.