Glad to see you are practicing! Great idea for getting the hang of shading, highlighting and blending. I think you are on the right track. His chin looks the best of everything so far. Try exaggerating the lights and darks a little, blending with the same graduating color values in between the two. And dont let anybody scare you off! Youre doing fine! :)
Oh yeah, I have a small off the comp. "homework" assignment for you to do. Take some objects from around the house - relatively simple ones - books, fruit from the fridge, stuff like that, and arrange them on a table under and to one side of a lamp, where the light source casts definite shadows. Just sit there and LOOK AT THEM. Mentally note where the shadows and highlights are. The next day, get a sketch pad and a pencil, crayola, whatever floats your boat, and roughly sketch it, concentrating on the darks, lights, and values of color in between. This will help you more than anything, I think.
Just one more thing - keep in mind that faces are extremely difficult to do, even for experienced artists. For your next drawing, try doing a still life of simple, inanimate objects.