The most important thing in lighting is understanding the layers of light...by this I mean the graduation
in ratios from key-light to shadow. Key light is your most powerful light on set, and the shadows can be
controlled by using a less powerful secondary and even lower powered tertiary light source to soften those shadows. For instance, the image of
Isabella Rossellini or as someone said "#3" (jeez!), appears to have perhaps an umbrella or B.Dish as the key light, and it appears from the catch lights in here eyes, her elbows are resting on a white fill card, which bounces light up to softly to fill in some shadows...notice under the chin...There may even be another fill source behind camera such as a few flash heads bounced into a white seamless, often referred to as a "fill wall". Backlights can be added for rim-lighting effect, or even the sun.
Avedon had a wonderful studio apparently, with skylights that had years of haze on them that filtered light
beautifully...but he knew how to light no matter where the subject was. He also shot a lot of 8x10...a friend of mine used to assist him, and often, he'd have an assistant compose for him on the ground glass as he stood next to the subject, studying them and gesturing to the assistant where he wanted the framing to be...
no yelling or loud voices...just calm peaceful direction.