When I design characters for myself, I think less about design than I do about personality. In fact, I rarely think at all about it. I feel it instead.
When designing characters for commercials or even for other people's cartoons, I rely more on design theories in the abstract. Like how to balance shapes and spaces that add up to a pleasing 2 dimensional graphic that is more symbolic of a general character type, rather than a fully dimensional multi-layered personality.
This is partly because I am designing backwards and partly because most producers, executives or scriptwriters don't want specific character designs. "Specific" features are generally considered ugly by authority figures in the animation world. I'm not sure why; perhaps it's just because traditionally so many animated characters have been generic symbols rather than true characters. I've learned to work both ways for different purposes.My most specific character is George Liquor. He is the only character that I've ever created all at once in a flash. His basic appearance and personality just popped into my head at the same time. I wish that would happen more often!
Usually my own characters start as an idea that rests somewhere between a general character type and a specific variation. Then I let nature nature take its course and allow the characters to evolve, being pushed along by the stories I write for them.
I give my own characters a lot more design flexibility than I do for characters for other studios. I let the storyboards, layouts, animation mold the designs - and vice versa. I don't think of each creative stage in a cartoon as a separate entity. I find that drawing storyboards is probably the most significant factor in designing a character's visual appearance and specific personality:
When I draw storyboards, I am free of the restrictions of too much consistency.