So, colors seem to me too much bright. Shading on hair doesn't quite blend with this style. The decision to make the background blurry took good but still, there are not enough details. Need more clouds. Book looks great. This
the cover looks in balance with shading.
Proportions for this style looks fine, the problem is only with the hand that closer to us that hold a book.
Glare on this chainmail looks chaotic, it needs some structure.
Glare on
eyes don't blend with everything else. It seems that you use effect for that. If you add some more little details on characters art will look better. But not too many details. The line on sketch looks undetermined, you need to be more determined when you hold a pencil, it makes you improve more effective.

I tried to be as objective as possible.