/ic/ - Artwork/Critique

My first attempt at drawing from imagination.

Right of the bat, fingers are fucking impossible. Even looking at my own hands didin't help.
I can clearly see that I fucked up the head and line width in some places. Faces are my Chilles' heel. I have to practise drawing them more.
I'm a total /beg/ and don't know shit about shading yet.

Can someone please:
> Point out proportion (and any other) mistakes
> Fix the head
> Tell me how to make a simple drawing such as this look more 3D
> Give me a link to a good tutorial about drawing hands or faces.
> Give overall advices

Thanks in advance.