Mystery author David Hewson talks about a technique he uses for getting into the heads of his characters. He listens to conversations between the on ordinary subjects, how they express themselves, what opinions they hold, how they react to each other.

It looks like a valuable resource, and I plan to try it.

Heck, I talk to myself enough anyway. It would be more interesting to hear from somebody else once in a while.

Most books aren’t silent movies. Real characters communicate. So writers need some way to recreate the dialogue between the people in their books inside and outside the book itself. Understand what I’m saying here? I need my people to talk to one another constantly, making everyday small talk that never finds its way to the page. I need them to live inside me before I can reproduce them to the world at large. There are few better ways to do this than to cultivate the habit of the interior conversations. Talking to yourself, out loud or in silence, in the character of the people you’re inventing The kind of habit that once got you committed to lunatic asylums when they still existed.

The whole post is worth a read.