After looking at this piece for a considerable amount of time, I have some points I'd like to give you.
You clearly have some fantastic imagination and inspiration with your use of colours and different materials which you have done well to incorporate into your piece.
I do feel however you could benefit greatly from some anatomy studies. Maybe try taking a small A6 sketchbook and pen out with you everyday and draw at least two people you see in quick succession. By doing this you will begin to get a better comprehension on facial placement, 3D effects and lighting. Also by using a pen you are less likely to want to rub things out allowing room for mistakes.
Mistakes are your friend!
I'm actually quite inspired by this piece to use more materials in my own art work at this present time.
To add to your technique and impact score, I would suggest using different materials, try experimenting with pencils, pens, crayons, ink and experiment! experiment! experiment! By doing so you will find easier and more exciting ways to create art.
Please continue to make art, and I hope my suggestions help you to improve!