It needs to be striking. It needs to be evocative. It needs to fit on a book cover, for novels, which is why you have a lot more leeway on the short stories for length on short stories. Subtitles can be nice for clarification, especially if the name is more evocations. Then, there's a certain tendency of self-publishing amateurs to go for subtitles, and often extended ones, so there's a certain danger of not appearing professional. They also may make the reader not pick it up, because of wanting a self-contained work -- or waiting for the rest to be released.
Above all, it needs to indicate the contents of the book. You need a very SFnal cover to get away with Dragon Ship as an SF book. One author talked of envying the musicians: Concerto in B-flat, as opposed to Space Opera with Explosions and Aliens.
An editor talked of Birdsong Stops, which was a noir-like book where the title referred to something that made the security guard highly alert, and which she had a murderous time convincing him that they could not use because it smells rather more of ecological disaster. Someone else proposed A Sudden Silence, and she wrote that down.
To add stories about how Bujold is terrible about them and there's no telling how many contracts had Miles Gets Laid as the working title, so as to threaten her with the possibility of publishing with that. Of course, we'd buy that -- or, for that matter, Ivan's Book as someone in the audience pointed out. (She said she's read Ivan's Book.)
Talked some about Heinlein's wonderful titles such as Citizen of the Galaxy. Then, there was Double Star. Probably part of the reason it's less known is the title is not evocative or distinctive. (I can remember the book from the title but not vice versa myself.)
A nightmare: Your title is accidentally duplicated. Mostly your near contemporaries -- the horror stories were published within a year, and within a month, of each other. Still, one editor told of how a book had gotten through the writer, the agent, and the editor with the title The Big Sleep before it dawned on the editor that there might be a problem there. Classics are wise to avoid unless you are ringing changes on it.
Character names as titles, which are no longer commonplace. Dickens had wonderful knack for names that resonated. It's not completely gone, though -- Jonathan Strange & Mr. Norrell harks back to the old days -- which is partly to underscore the old-fashioned elements.
The cover, which the writer can't affect, and sometime the editor even has difficulty with, is, alas, even more important than the title. One writer complained about the woman, full-clad, but with a full figure, and that only 14-year-old boys would read it. The editor told him that with this cover, his fans would read it, and so would the 14-year-old-boys. Horror stories about misprints, because you read what you think is there. A last name of "Fod" -- a senior editor held it up on front of the editorial staff and asked what was wrong with it. Or Rouge Queen, or Touched by Goo -- that later one suffered from a font that made its D too much like an O.
And I had a new idea for a title during it.