Tour of Sketchbook:
Here are some texture studies I did with markers. Each square illustrates a different texture. It's a great practice to see what can be produced with just a sharpie. A good challenge is to come up with as many textures as you can with one medium. Some of the most interesting works of art use multiple textures.
Planes also can creat demension. In my skull studies, I studied a skull and drew the flat planes that I saw within the object.
Eye Doodle Tutorial
I'm addicted to drawing eyes, and have gotten quite aquainted with how to quick sketch a realistic looking eye. Today I will show how I go about doing so. Feel free to take notes of what I do and follow along.