I absolutely love this advice from Walt Bogdanich, investigations editor for biz/finance for the New York Times, who's won three Pulitzers. He told a group at the Society of American Business Editors and Writers (this via a blog post from Talking Biz News) that you should be alert for when a source says something unexpected or note when you see something that seems out of place. There might be a story there.
An excerpt from the blog post: "Bogdanich doesn't decide to find a story within a subject, and he doesn't try to find a story in a massive database. He acts when he's inspired, and loves to look into what nobody else is ..."
My thought is, we do our share of "let's do a big story about (topic)" or "let's get this database and do a project on it." Setting out to do a story on a topic can be deadly because there is no true focus. You may be able to have more success extracting a story out of a database. But the best stories rise out of a reporter hearing or seeing something and asking, "Why is it that way?"
More from Bogdanich at the blog post itself.