Natural light portraiture is a popular choice for many. However, natural light has its limits and if you don't know how to manipulate that huge single stationary ball of light in the sky, you're most definitely going to produce less than satisfactory results.
In the hands of a professional, the studio becomes a canvas and the photographer the artist. The ability of the photographer to control artificial light is what sets him apart from the amateur. For example, classical portrait lighting consists of five basic lighting setups. Two of my favorites are Rembrandt and Butterfly (or Paramount) lighting. In my opinion, Rembrandt is by far the most beautiful lighting. The name is - as you may have guessed - inspired by the Dutch painter who created stunning and timeless portraits. Under this technique, light cascades across the subject's face at a 45-degree angle. This in turn, creates the familiar triangle of light on one cheek. However, there are other light sources engaged in most studio set-ups such as beauty dishes, soft boxes, reflectors, diffusers, kickers, and...Oh, sorry, I'm getting off the subject.
One problem with natural portraiture is that we more often than not, have one fixed light source to work with. On a sunny day the light coming from the sun is hard light - meaning it creates harsh shadows. You can't move the sun or wait for an overcast day, but there are ways you can make daylight work for you.
Try this simple technique: Grab a mirror and walk outside in the middle of the day. Look at the shadows on your face, paying close attention to where the shadows land. If you can, take a picture of yourself at this time. Now, wait till about an hour before the sun sets and do the same thing. Face the sun (slightly at an angle so you don't go blind) and look at your face. The differences will amaze you! There are other tricks such as "bouncing" sunlight onto the face using a reflector or even a white poster board or by adding supplemental lighting but the point is, understanding the principles of light is the first step toward creating an image that will end up on the wall and not in the trash.