One of the greatest things about animation is bringing life, expression, and emotion to an otherwise lifeless character. Part 2 in this series covers animation timing, staging, fluidity, and adding subtle movements to the animation.
To show how involved (or simple) entries can be - I've posted a couple sample "How To's" on the Animate This! Tutorial Challenge site (/en-us/contests/animatethis/contests.php). Have a look at the entries by Joe3D and Bob3Dguy on using constraints to focus eyes.