In my opinion, these are the most important factors in any character design: color, concept, shape, simplicity, cohesiveness, repeatability, personality and uniqueness.
Color: Any design with colors all over the place creates too many places for the eye to look. Keep your color design very simple and zen. Looking at the colors shouldn't be jarring or confusing. This isn't to say only use one color, not at all, but try to make sure the ones you use are harmonious. Avoid mixing and matching different saturations of the same color or picking colors that clash with one another.
My rule of thumb: Stick to no more than three base colors and some value variations.
Concept: Your design should have inspiration, even if the inspiration is just your intended character's personality or an interesting object that represents them. Your character could be a bookworm, and that would impact her posture, her clothing, her hairstyle...pretty much everything about her! You can design