Place the greens in an ample bowl and give them a preliminary light coating of oil. About 1 tablespoon of oil will suffice for a medium-size head of lettuce, or 2 cups of salad greens. Toss repeatedly by lifting the leaves gently with your hands or a large salad fork and spoon until each leaf is completely coated. This conditions the greens against the wilting actions of the vinegar. Follow up with more oil, then vinegar - in all, about one-quarter of the amount of oil - salt to taste, and further tossing.