1. "Block In" your composition by thinking in terms of LIGHT, SHADOW, and SPACE.
Use the side of your pastel to cover your page quickly with anything that appears as even a slight shadow, leaving only the lightest areas untouched.
Accurately defining individual objects is NOT the point of this step.
You are defining SPACE!!!
2. Work the background and foreground equally.
Treat important objects the same as unimportant ones as you develop at least three different types of darker gray.
What parts are supre dark?
What parts are the deepest, darkest parts?
What areas are in the middle?
Still defining SPACE at this stage of the exercise.
Still using the side and edge fo the pastel, conte crayon, or graphite stick, but NOT the tip of it.
3. Find the shadows that are 100% black.
Use the point of your pastel and really work those to make sure they are 100% black.
Ask yourself if you have left too much area of your page as pure white ("paper white").
A few areas might need a very light touch to make a light gray surface.
4. Now you can measure individual objects and adjust them for proportion/scale.
(remember, this is an exercise in space and shadow. That is why measuring individual objects is one of the LAST steps)
Use your eraser to bring out the few highlights that are pure paper white.
Drawing lines is optional.
You might want to leave the soft impression of pastel alone.
You may also choose to blend pastel with your finger to create and even softer feel to the drawing. (I'd caution you against over blending and making the whole thing appear "muddy")