This exercise starts with a weight drawing as described above. Go lightly at first until you have the main shapes blocked in, then continue over the form pressing heavier as you follow shapes that recede and lighter over forms that come forward. (Heavy into the groin, and light over the belly deep into the armpit and light over the chest etc).
Try and get the sense that you are pushing into clay; that you are moulding the drawing almost like a sculpture.
Towards the end, you may use the crayon or stick of graphite on its point and follow the deepest parts with these darkest strokes.
If you find yourself colouring-in a pretty picture you are failing to make the most of this exercise. Again, working from an upside down picture will help with discipline and will show you how much better a rendition will result when you concentrate on the exercise rather than the prettiness of your picture.