The following pictures and descriptions follow my drawing process for a drawing done with graphite in my sketchbook.
I start with a basic line drawing, attempting to make the proportions as correct as possible. After doing this, I use an eraser to lighten the drawing.
Next, I do the first round of shading. I target the drawing in sections first and then take some time to examine the different relationships between the shadows and light overall. I continue to correct proportions as I notice mistakes.
For this particular piece, I only added one more round of shading to "push" the lights and shadows within the piece. However, I will complete as many "rounds of shading" that I believe a piece needs. If during any round of shading I notice proportion issues, I will correct them as well.