One common mistake made by junior animators is to leave out eye darts - those rapid changes of eye direction that show that a character is thinking.
Or, the animator includes eye darts, but they are too slow and mushy to feel believable. So how do animators time eye darts? Eye darts should be super quick - ideally with no in-betweens at all.
To time an eye dart correctly, you simply pop from one pose to another, with a one frame cushion to ease in to the final pose. To see how to animate an eye dart, watch the video below.

