I read numerous books in numerous genres, watch tons of films, movies, and plays, but sometimes in order to fuel up the writer within, I just have to observe. Simple actions I witness during the day, are a powerful tool in making my characters believable and relatable. I've hit research mode in one of my current WIP's and everything around me is fair game. I noticed a kid pumping gas today into his rusty Cheverolet and he was chomping his gum just like a cow chewing its cud. For whatever reason, it was annoying as hell and a perfect fit for one of my characters.
I believe that everytime you see a gesture, motion, or action that speaks to you; you should WRITE IT DOWN. You can always use it or lose it later. An excellent resource for this is your Daily Newspaper. Sports pages are my fav. There's so much going on in one single action shot, that it begs you to notice every detail, and details are crucial to pulling a scene together. It's okay to get carried away in research mode, because you can always pick through the most unique details when drafting your story.