These, then, are the main rules in producing a good book title, as I see them. Exceptions and differences of opinion may occur. Also, these are probably more applicable to novels than to nonfiction or other types of books.
1) People must be able to pronounce your title.
2) People must be able to spell your title.
3) People must be able to remember your title.
4) (This one is more a personal preference, but...) Avoid titles that are already established phrases or cliches.
I have a novel called Tourist Attractions, which breaks rule #4. But I didn't originally call it Tourist Attractions--that was a concession after my editor objected to the title I had given it, which was A Friend Who Sees Ghosts. Her objection came from the fact that the ghost-seeing friend wasn't really the point of the story. This is true, but the friend is the catalyst of the story to some degree, so I'm somewhat inclined to switch back to the old title now that the rights have reverted to me. I, for one, would sooner pick up a book called A Friend Who Sees Ghosts than one called Tourist Attractions (one problem is that people keep leaving off the "s" at the end of "Attractions"--already the spelling is an issue).
I also have a novel called Houseboys, and this title worked when I discussed the story with my family. But when I began pitching it to people at the writers' conference, I realized they all said, "It's called what?", requiring me to repeat it slowly. Trouble is, while I and my sisters and my mom have all lived in sororities where they have houseboys, most people these days have not, and also don't use the word for anything else. All the same, it doesn't exactly break any of the rules, except maybe the spelling one on the grounds that people don't know what I just said and therefore can't spell it. I might change it; might not.
But let's move on to other people's books. I'll evaluate a sampling, from past Books Of The Day on a desk calendar I have:
The Known World: Not a great title. Vague and hard to remember. All the same, won the National Book Award.
Revolutionary Road: Good title. The alliteration helps it to be memorable.
The Jupiter Myth: Good title. Easy to spell, sounds intriguing.
A Company of Three: Not the best title, again for "vague and hard to remember" reasons.
She Wakes: Like Houseboys, looks all right written down, but when you say it aloud I bet you have to repeat it slowly so people know what you said.
L'Affaire: Ack! Foreign! Nobody can spell foreign stuff!
Family History: Not good; an established phrase already, and especially vague for a novel.
The Sword of Shannara: Bad title. I know Terry Brooks has made millions on these The __ of ___ titles, so my criteria are relatively worthless, but if you're an unknown, you can't expect to break in with a title that has a name no one has heard of in it. ("Shannara? Is that with one N or two? And how do you say it again?") Also, I get irked by these titles, usually of fantasy books, running 'The (Sword/Crown/War/King/Lady/etc) of (NonsensicalName/AbstractNoun)'. I like George R.R. Martin's series, but can never remember the exact names of the books. "A Storm of Crowns. No, A Sword of Thrones. No, it was A Feast of Kings. No, wait..."
Oh, and Professor Tolkien, The Silmarillion? HORRIBLE title. Nobody can spell it, pronounce it, OR remember it, unless they really spend some time committing it to memory. While we're at it, the character names need a lot of work. In online discussions, even people who adore the Sil are constantly mixing up who's Tuor and who's Turin, and who's Finwe and who's Fingol.
Yeah. So that's my philosophy and I'm sticking to it. But I'm unpublished, so what do I know?