First of all, Layers help alot
Second, you can add shading using the airbrush
Third, add two white dots to each of the eyes.
Fourth, Try using a thinner pen size, I've used pen size 4.
Lastly, I think that Firestar's fur should be more of a reddish orange colour.
Well thats about as much bits of help I can think of right now, hope it helped chintz!
