Drawing is not following a line on the model, it is drawing your sense of the thing.
Get the few main lines and see what lines they call out.
To paint is to know how to put nothing on canvas, and have it look like something when you stand back.
The picture that looks as if it were done without an effort may have been a perfect battlefield in its making.
A Curve does not exist in its full power until contrasted with a straight line.
Personal experimentation is revealing, and once you get into it, immensely engaging.