Mickey's ears are always the same shape
When you watch Mickey Mouse you can notice that the shape of his ears are consistent no matter at what angle Mickey is standing. This distinctive shape allows Mickey to be quickly and easily recognised, even at a distance.
When creating a character, keep in mind that it wont always be front and centre. If your characters are in the distance, in shadow, or otherwise impeded, a viewer should always be able to tell which character is which.
Another example of using distinctive features and consistent shape is the virtual band Gorillaz. The music is created by real people, but each member of the band is presented to the public as a two-dimensional illustration, (the characters are also animated for the music clips). Thought not as well-known as the image of Mickey Mouse, these characters are unmistakable to the fans. Individuality is in the form of hats, hair styles and other accessories. These thing are also smaller details than Mickey’s ears, (other than some of the hair), but when put in combination which consistency of shape they mark each character.
Gorillaz Album cover
42 GunSlinger 