The first thing your going to want to do is find a location with a window and position your subject so that one side of their face is being lit by the natural light coming in through the window. Once you find a good location be sure to turn off all unnatural light sources (lamps, overhead fluorescent lights, etc) as it is not good to mix different types of light. When you mix different types of lighting skin tones look unnatural.
In the example above, we used a window (outside of the frame on the left) to light the left side of the subjects face. This is known as the key light because it is the brightest light source. If you look closely, you can see that the left side of the subjects face is slightly brighter than the right side. This is because the window is coming from the left side of the frame and directly hitting the left side of the subjects face. Just outside of the frame on the right, we used a reflective white sheet, which you can find at any home depot, to bounce light coming in from the window onto the right side of the subjects face. This is known as the fill light. As you can imagine, this light source is not as bright as the window but can be used to fill the darker side of the face. In the example above, the intensity of fill light is almost balanced with the intensity of key light creating a very soft and even looking interview. When shooting business or corporate video it’s ideal to create a flattering interview look with little shadows and contrast, such as in the example above. You can do this by using a key and fill at similar intensity. When you have a higher contrast between the key and fill you create more shadows and a more dramatic look. This interview lighting style is more likely to be used for a bold look like on an athlete, mysterious character or in a cinematic story video such as in the example below.
In this example the fill light is much darker, and as a result the shot is much more dramatic.