Now that I'm animating, I turned to some of my favourite films for ideas on facial expressions and acting. These really help get me thinking about how far I can push my characters, as well as how to express certain emotions.
Dash is a really great character study because he's a manipulative brat and cute at the same time - studying him has helped me loosen up Bir's animation so that he's not so angelic all the time.
Looking at Elastigirl/Helen Parr helped me develop the mom into more of a character as well, instead of the stiff person I had in my storyboards. However, I've always found the animation on Elastigirl to be just a little bit awkward, so studying the animation also helped me dial into the elegance that I wanted in my character (of course, whether I'll succeed is another issue altogether).