i agree with pawige
the forms need to be better defined. right now things just flow into each other and u arnt able to tell differences between sections, or sometimes even what they are.
try to define more areas of the face and body instead of just what the outline shows. the outline is the simplest line in the entire piece.. The lines inside are what make the figure unique and interesting. Right now there is nothing, but a bit of lightsource shown.
I agree with pawige about looking at different skulls to find interesting forms you can use, or search aliens or something. But try to find an idea for a reference and then use that for inspiration.
it also needs better texturing
to me it feels like it deserves a hard - bone like texture. OR perhaps a cracked rough scale look would suit it aswell.
in order to do that though, you need to pick slightly more contrasted colours, such as pawige did and then after your lightsource (where shadows and highlights are) is established, then i suggest you work on texturing.
Remember though - texturing can be thought of almost like a gradient aswell.
the lightest and darkest shades have no texture - everything melds together into that solid colour
the next shades (second lightest and second darkest) have alittle bit of texturing starting to develop
after that, all the shades in between - your midtones - are what carry your texture. By using this method it helps to enhance form aswell, because then the shadows and highlights really stand out.
by using this method i think it would help when using a hard bony texture because then it would help to make a harder, defined look, opposed to if everything had a bit of detail it would look more soft and melding together
