Make sure your character is able to be "Indentified WITH." RELATABLE. You need to think about your audience, what they would indentify with, and put some part of that in your character...whether it be age, a common problem for that audience, or a common interest that audience has.
The character needs to be "INVOLVED." They need to be part of the action of the story, the verbal part AND visually part of the action. Do not make them a passive bystander watching the action in any way. They must be IN it. INVOLVED.
And finally the character needs to be "INTERESTING." Something about them should be unpredictable. Instead of a cat for a little girl's pet, give her a bearded dragon. (see below)
In addition, ask yourself these three questions... WHO? WHAT? WHY?
Often the answers to those questions will provide you with a picture book story ready to go. For example...
WHO? Archer Aardvark, boy, Aardvark animal, age 5
WHAT? favorite color Orange, wears a baseball cap, loves baseball, needs his blankie
WHY? REALLY wants to play on the baseball team
So the story is... Archer Aardvark wants to play on the baseball team, but he can't give up his blankie. He tries all sorts of ways to play baseball WITH his blankie and finally figures out his problem in a fun way.
Then we talked about capturing the essence of an animal or person and then adding interesting things to visually create the character. I can't put the whole presentation here, but that's the gist.
Now, go create your own character and picture book.