Here's a messy little edit:
I think the first thing you need to think about is how you start your pieces. I see jagged shapes. Jagged shapes are good, but jagged forms are better. You want to lay down those forms to get a feel for how your piece might look and act in a 3D environment. That cloak, for example, is probably a thin rectangular piece of cloth that is caught in the wind, and I assume this because that's usually how cloaks work. HOWEVER! it could also have a funky cut on the bottom that goes up and down like a sine wave if I look at it differently. It could also be some crazy weird shield thing that he's holding—I don't know for sure unless you tell me. One goal for any piece of art is clarity, and it would take a lot more creativity to see something other than a rectangular cloak in the wind if you tried to capture how light would hit it in the real world.
Also remember that a piece of art is not the sum of its parts; a piece of art is an entire entity in itself, and should be treated as such. Right now it kinda looks like you made your zombie like, "That's an arm and that's a leg and that's a cloak. I will draw an arm, a leg, and a cloak." Try to think, "A zombie has arms, legs, and a cloak. I will draw an arm, a leg, and a cloak, but I first need to know how they would act around each other. Would the arm be in front of the leg? Would leg hit the cloak? How would I draw that? How could the jaw affect the collar? Would the arm cast a shadow on the cloak?" You want to create a wonderfully unified character; to do that, you need to understand how the piece works as a whole, and not just accept it as a sum of its parts. His pose, for example, looks almost impossible. His body seems to be facing the same way as a the viewer at the legs, but then goes completely perpendicular to the viewer at the torso. How would that affect the spine? Is that pose really impossible? The more you study and analyze the whole, the more unified you'll be able to make your art.
For the hair, ask yourself these questions; what kind of hair is it? Where is each cluster of hair? Which one is furthest away? Which one is closest? Would one cluster cast a shadow on the other? How does the cluster's position affect the lighting? The best way to answer these questions is to look at pictures or out the window, and try to see how stuff works. I hope this helps!
