A hook is anything that makes a reader want to read more. Hooks are generally found at the beginning and ending of scenes and chapters. They are what give you the cliffhanger feeling.
Most of the time hooks are questions the writer intentionally places in the reader’s mind. Probably the most common is, “What’s going to happen next?”
Having been both panned and complimented for my hooks, I think I have a reasonable idea of how they work. The best hooks seem to come from something substantial in the story itself. The questions left in the reader’s mind will involve something to do with the characters motivations, goals, or conflict.
There are always elements about a story that are simply too big to fit in. It seems to me most new writers react by simply telling it. These over-sized elements are excellent sources of hooks, provided you show instead of tell. For instance, a spy who may be a double agent can provide plenty of hooks, so long as you never come out and say she is a double agent. Leave the reader wondering – is she, or isn’t she?
Withholding important information does not necessarily make a good hook. A lot of times it will simply backfire by leaving the reader confused. If a character is behaving oddly because he is a werewolf, and you don’t get around to saying he’s a werewolf until page 150, then most readers are going to get frustrated and pitch the book. Withholding a pet’s name without a very, very good reason will backfire. Withholding all of a character’s motivation or goal will backfire. Withholding some, on the other hand, can be tantalizing.
The point is you have to give the reader enough information for them to make some guesses about where the story is going to go. Keeping back too much undermines the real hooks.
When you do set a hook, it should be with an eye to the theatrics involved. Unveil the answer to one question, only to leave the reader about another. You could say the double agent DID put a sleeping powder in the hero’s soup. But she didn’t intend the soup for him. So who did she intend it for?
Don’t ask the question for the reader. Leave it hanging out there and let the reader come up with the question on her own. Don’t be to quick to answer it. But don’t wait to long either.
It’s a matter of balance between how much you reveal and how much you hold back. A lot of the time setting and releasing hooks is a matter of feel. As they say “always leave them wanting more.”