A page from class showing line drawing exercises and warm ups both invented and from observation in a favorite medium combination. With ballpoint pen I am unable to erase and it's the most freeing way to start exploring in drawing. If my pad is still thick underneath (I buy this newsprint in A4 size pads at USAVE) it provides an extra layer of cushioning and the combination texture and feel of the point is exhilarating!
Line is one of my favorite topics for a class. The integrity and confidence of your lines are what are most often the first marks made and can usually be seen (palimpsest) in the end also. Correct drawing is dependent on this.
Try to observe and track your lines to the edges and shapes you actually see, this may be even the softest of form changes. The result is a painterly treatment in line I call a lightmap. Dark and light areas are clearly indicated, and "mapped" out. This is especially helpful when painting in watercolours. Your light and dark values when delineated this way can lead to a strong composition.