Once you have draw the basic line,shape, and form, then you are ready to shade.
I will add a light gray using a 2B graphite pencil. I will leave some areas of white where the light is reflected.
I will add the next darker value by shading with a 5B pencil.
I will continue to add my next darker value to all my forms using a 5B graphite pencil.
I will continue my shading with a 5B pencil.
Continue shading with your 5B.
Clean up and touch up.
I will create a cast shadow depending on the direction of my light source.
I will create a horizon line and shade my background.
Darken and add shadows.