A good concept for dialogue in animation is " Inflection". The back & forth, forward-side, swivel-swivel, or side to side, Emphasis or comfortable speaking we all do most of the time. The best example for this, of a broad effective type is in "Jim Henson's Muppets". Here is a fantastic skit of this idea in action from the masters, w/ Fozzie (Frank Oz), & Rolf (Jim Henson).
They get in their character so much, that the acting, fun of discovery, it's 2nd nature( done w/o thought) and just looks natural. There is no actual piano there in front of them, yet pretending to hit the keys, in sync as if it was them. Them same applies to them speaking to the very simplified, to just the mouth opening and closing, head tilts to get the point across. Very entertaining.
- Also side note: I was fortunate to see, that all though the muppets franchise has been sold to Disney. The tradition of real puppetry lives on with Hensons actual Troupe still staying strong on stage, doing shows( too bad they cant use Kermit and others) but what I noticed was the skill and quality that definitely shows through. Here is more info http://www.henson.com/alternative.php?content=puppetup