/ic/ - Artwork/Critique

So I've got my art to this point but I'm not sure where to go from here. Obviously there's a lot of things I need to improve on but I feel like I'm being pulled in too many directions.

Should I focus on learning how to shade/render? Or should I learn more about how to sketch/do lines? Or should I just keep working on my construction (as you can see I can draw people from the front a lot better than the back, and my ability to draw heads/faces is pretty bad).

I guess what I'm saying is that I don't see a clear direction to go in to make the "next big improvement". What's the most valuable skill that I could learn next?