Avoid Flat Color and Geometric Shapes

If you want a good grade, avoid simple, trivial illustrations using flat fills and geometric shapes.

This artwork has a trivial, childlike technique that won't get much mileage in any portfolio (or for a grade).
Avoid this kind of style when working in Photoshop (or in Illustrator too, for that matter!)

     
The style is very basic. At least there's an attempt for perspective. It's still
not enough though.
Not enough here to interest anyone.
   
Very child-like illustration, no real concept. They left room for text, but that's about all you can say about this.