Quick little tip I wanted to post. One of the biggest issues I see with people first starting animation (and especially when animating dialogue) is they don't think of the whole face as a unit. And I was a victim of this as well when I first started. I needed the characters' mouth to open, so I grab the jaw controller, open it up and move along. Not once thinking about how the face works and how its connected. Open your mouth as wide as you can right now....what happens? You probably widened your eyes, raised your eyebrows, your mouth corners pulled in...the whole face is involved. Think about the face as a whole unit, not just one jaw controller you open & close - it will breath so much more life into your animation.
Quick and dirty example I made - see how much more life there is once you start involving the whole face