Let me start out by saying it's awesome to hear that there are school assignments that require pixel art!
You seem to already have a good grasp of lighting, which is nice, and your character does have some personality. However, I feel like you could push the amount of personality way further.

The thing I found most lacking was the pose. She's just standing straight up doing nothin'.
Here I've drawn a stick figure over your image with a more 'dynamic' pose (pretty generic female pose really).

Then I just rolled with it.
Added a little more contrast so I could define some things more.