As Seanan and Ed both quite rightly point out, the title has to be interesting, evocative and emblematic of the story, without trying too hard. That might mean short or even brutal in some cases ("Going Bad"), or downright poetic in others ("Mr. Scalpel and Mr. Gloves and the Cancer at the Heart of the World").
I believe I've discussed this before, but here's Jay's handy cheat sheet for titling short stories. I suppose it works for novels, too, but having written 450 or so short stories and only about a dozen novels, the issue comes up far less often with book-length fiction.
- If the title is self-evident from the nature of the story, I go with that. ("The American Dead".)
- Sometimes the title was the original germ of the story idea. ("Lehr, Rex".)
- Sometimes it's a memorable line from within the story itself. ("The Sky That Wraps The World Round, Past the Blue and Into the Black".)
- If none of the above works well for me, I go to either a Bible search engine, always selecting the King James version, or a Shakespeare search engine. I enter a few keywords from the story, retrying that search several times with different keywords or concept terms.