So I hope you'll understand that I'm not pretending to give some kind of expert lesson on how to come up with a title (and if anyone knows of one, please point me to it). I just want to discuss some of the problems I've had, and some of the solutions I've found — as well as a few examples from classic books — in the hope they'll be useful to someone.
Broadly speaking, there seem to be three kinds of titles: descriptions, allusions and quotes. Literal descriptions are the easiest, when they work, but they can risk being flat and pedestrian. They're best, perhaps, when they're both descriptive and evocative. Lord of the Rings is just the designation of the main antagonist, but it's a haunting phrase and makes an effective title. Michael Moorcock's Stormbringer is the name of the hero's sentient sword, but again it's a name that can send shivers up the spine.
Two of my available books have descriptive titles, though treated in slightly different ways. The Temple of Taak-Resh is a light sword & sorcery tale set mostly inside the temple in question (Taak-Resh being the god it's dedicated to). This was one title that gave me very little trouble. Once I'd established the setting, it seemed an obvious way of evoking that slightly old-school S & S feel.
By contrast, The Triarchy's Emissary is descriptive (it defines the main character) but more mysterious. The working title for this one, as far as I remember, was Assignment in Faiz (the city it takes place in) but that felt a bit clunky and gave the wrong vibe, more like a spy-story set in the Middle East than fantasy. The Triarchy is something the reader learns about in the course of the story, and working out in what sense the character is its emissary creates tension.
The Treason of Memory went through its entire first draft, and a good deal of its revision, simply called Estent, the main character's name. There seemed no obvious descriptive title, so I had to sit down * and work out what the thing was actually about.
For one thing, it was a political thriller, though in a fantasy context, about a plot against the kingdom, so treason would be a good word to get in there. It was also about the main character's memory being tampered with, but there seemed no obvious way to link the two. Except that he's been let down — betrayed — by something we're used to relying on. The treason of his memory. The phrase fell into place, and I knew I had the right title.
Steal Away appears to have been a little easier. I used the main character's name during the first draft, but I seem to have found the right title as soon as I'd finished that. This one is something of a pun. The two central characters are carrying out a burglary so they have enough money to get away from the city they're in — steal… away. It's also very possible that at the same time I was thinking of a line from Robin Williamson's lovely song "For Mr Thomas": Let us steal away whatever we're supposed to steal. That can happen.
Sometimes, a title can have multiple meanings and be both a description and an allusion. Return Switch, an unpublished story, describes a piece of technology (magical tech, that is) that's crucial to the story, but it also refers, quite separately, to something that happens at the story's climax.
In the 19th century and before, the literal title was most common (think of all the Dickens novels whose titles are just the main character's name) and it's still found widely, but the allusive title has become more popular. An early example is Henry James's The Turn of the Screw, which refers to what's figuratively happening, rather than anything literal.
Sometimes, a title does refer to something physically and literally in the story, but its symbolism far outweighs its literal presence. In James Branch Cabell's Figures of Earth, published in 1921, the main character does in fact obsessively make mud figures, but this is hardly the main plot. More to the point, the book is essentially about how we obsessively create a series of fronts for the world to see us: It is the figure of a man, which I have modelled and remodelled, sir, but cannot seem to get exactly to my liking, as the hero puts it.
On the other hand, a title can refer purely and simply to the mood of the story, rather than the plot. Perhaps my favourite example of this is one of Karl Edward Wagner's Kane stories from the 1970s. Who would expect a straightforward (plotwise, at least) sword & sorcery tale to be called Reflections for the Winter of My Soul? And still less for the title to work.
A third approach to creating a title is to use a quotation, which may mean something in its own right but gains far more significance if the reader understands the context of its source. At An Uncertain Hour (a title the novel certainly didn't have in the earlier stages of its creation) is taken from Coleridge's The Rime of the Ancient Mariner, and the whole comparison between the Traveller and the Mariner is crucial to understanding the novel's theme. On the other hand, it also has a literal aspect. The plot jumps around between multiple time-periods like the Doctor on speed, and much of the time the hour really is uncertain.
I've used quotes for a few other titles (Ancestral Voices, also from Coleridge, and A Deed Without a Name, from Shakespeare) but this approach was especially common in the earlier 20th century, though it goes back at least as far as Hardy's Far from the Madding Crowd (Thomas Gray). Well-known examples include For Whom the Bell Tolls (Donne), Tender Is the Night (Keats), Brave New World (Shakespeare), Of Mice and Men (Burns) and many more. A recent fantasy example is Abercrombie's The Blade Itself, a phrase taken from Homer.
Sometimes the meaning is clear enough even without the original context, but at other times it's completely incomprehensible. J. M. Barrie's play Dear Brutus, for instance, has nothing whatsoever to do with Romans, or even with assassins. It's about characters who are all unhappy with their lives and are magically given a second chance, only to find they make exactly the same mistakes again. The title comes from the scene in Julius Caesar where Cassius tells Brutus The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.
Of course, this risks turning into an elitist guessing game. In my case, I've tried to avoid that by quoting the relevant passage at the front of the book and giving all the information readers need to look the rest of it up. If they choose not to — well, I can't force them.
There are a lot more subtleties than this in finding titles, but hopefully these ramblings might give you something to go on if you get as stuck as I do with them. Fundamentally, though, any title (unless you're lucky enough that it comes to you fully formed) has to start with asking yourself what the story is really about.
Other than about four hundred pages.