Beautiful images are made of a mix of great ingredients. A beautiful model, a great pose, and wonderful lighting.
If we look at great photos portraits (go see the Sue Bryce website, for example) we see great lighting. Light is such a key factor in creating great images, and soft light is the key to creating great portraits. The softness of light is determined by the size of the light source respect to the subject. Large lights create soft, wrap-around light with soft shadows. Small light sources create sharp shadows. Is the sun a soft light? No. The sun is a very sharp light and so it does not create flattering portraits. Ask any photographer and she will tell you how horrendous is sunlight for portraiture.
If you had to think if the sunlight is soft or sharp don’t worry. A lot of people don’t answer that question correctly. It’s part of not being trained to observe the light.
I have a fun, easy exercise to suggest for the next few days: every time that you see a light source find out if that light source is soft or sharp. Once you determined that, notice if the light is large or small, in proportion to the subject. Here is a hint: the sun is huge but, because of the distance, it’s a small light source and so its light is sharp. Learn to recognize the difference between window light, candle light, lamp light and so on. By becoming aware of the light type we learn immediately the differences between each light type and the mystery goes away. We learn how to use those lights in our work.
If you spend some time observing the light your understanding of how to use it in Poser, DAZ Studio, Reality and LuxRender will improve quickly.