From Bert Dodson's Keys to Drawing:
There is a scene in an old Western film in which Danny Kaye, as the hero, is challenged by a dangerous gunslinger to a shootout in the street. As he walks toward the saloon door and into that street, well-meaning friends give him advice on his best chances of surviving. "The sun's in the west so keep him to the east," says one old-timer. "He stands up tall, so squat down low," says another. Someone else advises, "He shoots from his right, so lean to the left." Kaye desperately tries to remember these tips, but by the time he reaches the swinging doors, he's hopelessly confused, and we hear him muttering, "The sun's up tall, so lean to the west...he squats to his left, so shoot down low...he's east of his right so shoot at what's left..."
Drawing, if approached as a set of instructions that must be remembered, can make us react very much like Danny Kaye in the scene above. No one I know draws that way because it is difficult to keep such a jumble of instructions in mind while drawing. Simply remember that there are many keys to drawing...With use they will be absorbed into your own system of drawing. We cannot bring to bear all our knowledge at once. What we can do is concentrate on our subject and trust our eyes.