Personally, I'm lazy. I look at what I need, fill it with a stereotype, then fill in some traits that break the stereotype. It gives the readers someone they can identify with, but it makes for nice little surprises through the story as well - just when the reader thinks that they've fully figured out the character, they see something new. For a mystery story that I'm writing, I have the good ole, hard core NY cop who's been there, done that, doesn't care what people think of her, is divorced from her husband and is trying to cope with a slightly too grown-up teenager. And when the going gets tough, the tough get ... a facial. She doesn't need to have the biggest balls in the department; she simply needs to be the best detective in the department. She sees no reason why she can't be the best while remaining a woman. I also try to give each major character a quirk. I cheat here, too. I've got so many quirks that I just select one of mine at random and give it to the character. (I suspect that I'm slightly obsessive-compulsive. I've racked up idiosyncracies like business travelers rack up frequent flyer miles.) So, what's your secrets to character building?