I spend a lot of time watching people. It's free and relatively safe if you're good at it. Once, I was sitting on a bus trying to read a book. Directly in front of me sat a couple who couldn't keep their lips off each other. I was getting a little annoyed when my eyes suddenly caught a man standing in the aisle giving the loving couple a huge dose of “stink eye.” It was gold. For the remainder of the trip, I watched this sour old man and played with different back stories and scenarios that led him to be this put-off by a couple of young lovers.
Local theatre is also good reference. Watching live actors is incredibly inspiring. You see what works and what doesn't, and you also see why. Movies are good, but there is so much care put into them that it's not always as rewarding as live theatre. Movies lack a certain energy and transparency that makes live theatre such a valuable reference.