It's hard to overstate the importance of a good book title. The sales of a book often hinge on that critical element of authorship. Generally speaking, the better the title, the better the sales of the book will be.,
Consider, for example, the original and eventual final titles of the following books, and ask yourself what might have happened to those books had their initial titles been used instead of their ultimate titles.
Original title Ultimate title Author
First Impressions Pride and Prejudice Jane Austen
All's Well That Ends Well War and Peace Leo Tolstoy
Tomorrow Is Another Day Gone With the Wind Margaret Mitchell
The Last Man in Europe 1984 George Orwell
The Sea Cook Treasure Island Robert Louis Stevenson
Prometheus Unchained Frankenstein Mary Shelley
The Fireman Fahrenheit 451 Ray Bradbury
It's hard to guess as to what the sales of those books might have been had their original titles been retained, but I think you'll agree that their ultimate titles were great improvements.
A good title must appeal to the eye at first glance and "hook" the potential reader (or purchaser). It must be, as they say, "eye-catching." Those few words--supplemented, of course, by a well-designed cover illustration--must make the prospective purchaser want to snatch it up for a closer look at not only the outside of the book but also its internal contents.
A good title must also indicate in some way the content to be discussed in the body text of the book. The title is, in a real sense, a promise to the reader, so the writer must ensure that the title is true to that promise by delivering what the title suggests.
Shorter is generally better. No more than five words, preferably less if possible. Some famous titles consisted of only one or two words. For example, 1984, Frankenstein, Treasure Island, and Pilgrim's Progress. Sometimes, to ensure that a short title is more effective and not misunderstood, an author will add a subtitle. For example, The War: An Intimate History, 1941-1945, American Sphinx: The Character of Thomas Jefferson, and Dutch: A Memoir of Ronald Reagan.
Moreover, a good title must be memorable, easy to say and understand, and include key words about its contents (especially so during this age of google searching!).
Rather than choosing a title too hastily, good authors brainstorm all sorts of possible titles. They narrow the list, culling out some until they find the best one. Until one has a good title, he or she isn't ready to submit the manuscript.
Knowing the importance of a good title, I've spent hours, days, even weeks mulling the various possibilities for a good title for one of my manuscripts. The text is ready for submission, but I don't yet have a good title, so the manuscript is not ready for submission. I began the search even before I had written the first word of the story, and I've continued brainstorming long after I had completed the manuscript.
That's where I am right now with that one manuscript. It won't be "born" until I have the right title. I'm sure that it will come--eventually--but only after an indeterminate period of gestation and a lot of labor! Stay tuned!