Balathustrius: Yeah I think mixing up the direction can be really finicky. I think it works well when you are blending each layer as you go, otherwise it will add a lot of texture that you might not want.
The good thing about only going a single direction is that the viewer can see it as just a block of shading without minding the texture so much. I treat it like watercolor, where I lightly trace out the boundaries of the shadows and then hatch them in from largest to smallest.
Alright, I've got something I've been working on to understand the form of the face better, but I'm having a lot of trouble getting a good image of it online. My scanner seems to have trouble with pencil, and the pictures coming from my camera aren't too much better. Does anybody have any tips for scanning in pencil?
Anyway, here's the best I could get: I think I need to understand the form of the lips better - they don't look right to me.
jarathor: I missed your image somehow! Is it from observation? If so you can understand the lips better if you look at them and map out the areas of shading that define the lips, without using any preconceptions of what they should look like. Try not to draw any hard lines at all unless it is exactly what you observe. Imagine you are simplifying it into a stamp for printing. Lips are difficult for me too, but it does get easier with practice.
Also, eyes aren't usually very white unless they are in direct light. We tend to see them as white, but they are usually a medium to dark grey, tinted by color of the light source. Natural lighting will often make the eyes a blue grey, where as incandescent bulbs will give them a yellow/orange color. If you leave the eye too light in relation to the eye-socket (which also tends to be darker than we perceive it) they come out looking over-large and a bit illustrative (which isn't necessarily bad).
It is hard to say without seeing the reference, but probably the part of the face and neck which are in shadow would be a lot darker. The is especially true for the eye sockets and under the jaw-line. The shading is a bit homogeneous now which I think is hurting the roundness of form.
Scanners... I know my scanner does this annoying thing with levels, by auto-adjusting the levels when I scan, which makes pencil drawings look like total crap. If there is a levels option in the scanner preview, drag the black arrow all the way down, the white arrow all the way up and the grey arrow exactly to the center. There might be 'output' arrows too which you should drag all the way out in the same way. In my case, if I hit preview again it changes the levels again and I have to redo it.