Hooks-- too many opening hooks seem designed not to open the story but rather just to have a hook-y first line.
But we all know that hooks sell.
The problem is, often the hook just confuses, because it's meant not to let the reader in on what's going on, but to be clever and cute and use buzzwords, or set up some ironic contrast, or... well, hook the reader.
Too often I read first lines that are "hooks" and then the story actually starts, and that hook just serves to confuse. It doesn't lead into the opening of the scene, or set anything up beyond the hook itself.
The first time Aragon saw his future mistress, he was knee-deep in naked women. (Hook) The victory celebration was held in the Headless Pig tavern on the outskirts of town. When Aragon entered, he saw two of his friends from the regiment standing at the bar, glasses raised-- (Opening)
Now notice that there's a break in continuity-- presumably the hook event (meeting mistress) happened AFTER the opening event (Aragon entering tavern). That's not necessarily bad (the hook might be sort of a topic sentence previewing the point of the whole event. But the discordance of sequence might matter, might confuse the reader, and so that should be something you notice -- there are always tradeoffs, and a common tradeoff to starting with a hook is that you mess up the chronological sequence of the scene.
Also how would you feel if you were the reader and you read that hook (where there's "mistress" followed immediately by "naked women") and assume sensibly that "his future mistress" means the woman who is to share his bed... but it turns out the "mistress" is actually his future boss (the mistress of the estate where he becomes head gardener or something)? Would that be fun for you, or annoying? Again a tradeoff-- misdirection can work to set up a theme of deception, or it can, um, annoy the reader by being deceptive. That is, you might think about whether this is amplifying or setting up something beyond just the cleverness-- and again, what are the tradeoffs?
Another danger is that you design the opening scene NOT to introduce the protagonist, set up the situation, hint at the conflict, all that good book stuff, but to provide an "answer" to the "cute question" the hook has set up. For example, that "knee-deep in naked women" is a good phrase, but if the scene is designed mostly to get the women in the bar to take their clothes off and lie down on the floor, the hook has actually harmed the coherence of the story. The opening scene should do more than develop the hook.
I think most of us can tell when a hook is designed just as a hook, when it isn't integrated into the story. That can work for some comic stories where you want to keep the reader off-balance. It might also work for some thrillers (oddly, I keep realizing that in many ways, thrillers and comedies are similar in structure, I guess because both are meant to provoke an involuntary response). But "begin as you mean to go on" is usually a good guideline. If the rest of the story isn't provoking, dislocating, deceptive, comic, clever (and most aren't, and aren't meant to be), a hook might be false advertising.
The best hook might not be self-consciously clever, but a first paragraph that intrigues in a more subtle way. (BTW, those of you who like to write in deep POV, hooks are seldom in deep POV. They tend to be more omniscient because they are often sort of an ironic comment on the situation-- and irony tends to be omniscient.)
If you must have a hook....
I'd suggest trying to write the opening scene to set up the situation, introduce a major character, start the conflict-- the usual opening purposes. Then, once that's done well enough, then read it over and let the hook derive from the scene. What's a major device in the scene, for example? Hooks often play off some opposition or conflict or unconventional take on the situations. Like if your protagonist is quite old, but will be acting like a baby (whiny, adorable, whatever), the hook might be something about: Tom was the oldest baby in the nursery. Okay, hooks are NOT my forte, so don't expect much in that line from me. :)
Sometimes you have a great hook and just can't help but use it. Heck, I've known writers who have come up with a hook-y first line, and then written the book around it. A couple thoughts then-- write the hook. Put it away. Write the book. Go back to the hook and make the hook and the book fit together. That is, make the book work without the hook, then make it work better with the hook.
Also, the hook, if you insist on using one, has to be honed. It's actually a bit of poetry, isn't it? It's impressionist rather than expressionist. Also, a hook will usually involve (like poetry) some word play, some language-pleasure, a pun or a twist on a cliche. You can't waste a single word in a hook, so experiment with different constructions and word orders. and don't forget the connection of "hook" with music (a lot of pop songs have a hook)-- balance and rhythm have to be perfect for a hook to work.
But you know, just as you have perfect pitch or you don't, you probably can either write hooks or you can't. Don't force it. Most stories are not going to benefit from a hook opening, so first make sure that the book should have one, and then make sure you're capable of creating one. (No shame in not being able to... hook-writing is a minor talent, not a major one.)
One other thought-- hooks can sometimes be used in query letters and the synopsis, even if they don't work in the opening scene.
Just never lose sight of what really counts- the story, the characters. Don't let any aspect, especially a hook, detract from that.