The Art Lounge

[Baegal]

It's also really important to consider simplicity and life.
You want a design that's very flexible and open to interpretation (sometimes)--one that can be drawn by memory by people who've seen it before,
like when someone says, "draw Spongebob" or "draw Pikachu". It might not be exact, but there are always key details people catch that help craft the character like Spongebob's squareness or Pikachu's red cheeks and lightning tail. Those details are the one you want to focus primarily--it's what sets your character apart from the rest.

It also depends on what you're going for. Having a simple yet effective design sticks in the viewer's head and also saves you if you have to keep redrawing it for animating or comics, but sometimes detailed works really effectively for things like final bosses or huge things.

Movement and life is also really important in character design. It could be the design is good, but the drawing lacks life and makes the character look boring. Exaggeration helps in both bringing life and adding character to your design (think of Eggman's body proportions, or Chowder's facial expressions).

When it comes to color, just try to get a palette set so you don't have too many unnecessary colors. Unless it's part of the design, rainbow color schemes tend to be overdone. Try a balance between saturated and unsaturated colors. Having everything too bright hurts the eyes, but you don't want everything to look muted either.
(Again, unless that's what you're going for).

Bottom line, design is really flexible and there are a lot of factors to it.
Do multiple drafts--try even drawing the character from memory the next day and see what sticks between both drafts.
Ask other people to draw him/her/it to get a fresh outlook.
Keep practicing--if a design doesn't work, maybe parts of it can be used for future designs!

Good luck! o/