Picked up doing charcoal portraits over the summer.
Charcoal medium demonstrates how shapes and shading is more important than details in a painting:

My sketching process step by step. Step 1 identify key points to preserve the shape:

Step 2 draw the points and form lines for reference, then add a few identifying elements:

Step 3 develop the drawing in reference to the lines:

Step 4, add different levels of shading to create depth:
