Don't think about how your characters sound, but how they see. Watch the world through their eyes - study the extraordinary and the mundane through their particular perspective. Walk around the block with them, stroll the rooms they live in, figure out what objects on the cluttered dining room table they would inevitably stare at the longest, and then learn why.
I always took pictures, but about five or six years ago, I started taking more behind the scenes at SNL, and now I have some 60,000 photos sitting on my laptop.