I want my titles to intrigue, tease, and give a good flavour of what the story could be about. It is particularly crucial to get the title right for flash fiction given in some competitions, the title is part of the word count allowance and for others it is not. So it always pays to check the competition details carefully.
I keep my titles fairly short (e.g. Calling the Doctor) as I want to maximise their impact. They're also easier to remember that way!