I have no idea how to write the perfect hook, or even how to write one at all. In my experience, either the first line comes out interesting or it doesn’t, and gently tweaking it doesn’t seem to change which one of those it resembles more. Since the hook is one of the most important if not the most important part of the book, this can be kind of unnerving.
Unfortunately, a hook for a novel is a little more than just that first sentence, and it is that important. People look at the cover and the title, and if they like that they’ll pick up the book and read the synopsis on the back, and then if the story looks promising they’ll read the first page. If I’m lucky, they read a couple more before making a decision, but usually one page is enough to tell the reader if they like the writing style or not.
Like the cave in the picture, a hook should be friendly yet mysterious. It should say “Interesting things will happen if you go further.” Not literally, of course, because that would be a boring hook.
A hook should also establish the story. It should show the tone, indicate the genre, and usually introduces some important element of the story like the setting or the main character or the scenario. Without a good hook, the audience will be lost from the first page and that’s not a good thing.
Fortunately, I’ve found that having the perfect first sentence is not the end-all to writing. Not that it should be skimped on, but it is something that can just be “good” or “decent.” The best books have gripping openers, of course, but it’s the page as a whole that needs to be well-written for longer works.
I find that comforting. Even if I mess up on that one sentence, I’ve got a little time to make up for it. It needs to shine, but it doesn’t have to blaze like a bonfire. Little candles are okay, so long as they’re what’s right for the book and for the audience of said book.