I recently had a question from a reader on characterization: You always say listen to your characters, right? What about when you are starting a book and you don't know them -- so you don't what they would or wouldn't do? How do you know you're on the right track? Or do you?
When I was first starting the Raine series, the characters came first and then the story started to follow soon after. So it was a journey of discovery for me and my characters. I knew Raine pretty well already, and through her, I got to know Tam, Mychael, Piaras, and Phaelan. Kind of like a friend introducing you to their friends.
But having Raine introduce me wasn't enough to get a complete sense of who the other characters were, their motivations, and basically what makes them tick. I'd always read about literally interviewing your characters, or figuratively taking them out to dinner. I've tried both, and it worked for some characters, but not for others.
I do have a tip for you on the "dinner thing" -- if you want to have a dinner date with one of your characters, let them pick the restaurant. Because subconsciously, you know more about your characters than you think you do, and that'll show in the kind of restaurant the character chooses. For example, Sarad Nukpana does not do burgers. His preferences run toward dimly lit, elegant, with a somallier that he can enjoy intimidating. Piaras loves a good burger (actually three burgers, he's having another growth spurt), and Phaelan will go anywhere where there are gorgeous waitresses. He'd be a Hooters man for casual dining, but a private gentleman's club for fancier fare.
Once you know the type of personality you're dealing with, you put your characters in the scene you have in mind and turn them loose. They'll take it from there.