The most important part of lighting a green screen is knowing what the finished product will look like. This should take into account the color temperature of the light at this point, because if the subject is supposed to be outside, then the light is very orange, and it will be hard to fix in post. It is also important to know the source (direction) of the light. One problem with poor green screens may be that the light is facing in two directions. For example, if the shadows on the subject fall right to left and the shadows in the background plate fall left to right, it will look very odd.
It is also important to take into account the shutter speed and aperture. For most film and video, the standard shutter speed is about 1/60th of a second. This creates what is considered the most natural motion blur. Technically, however, shutter speed is also defined by the amount of light. It is important to use a shutter speed that matches with the rest of the film, and creates the right amount of motion blur. Too little motion blur may cause the image to look jittery, while too much can affect the key. If the green is blending into the subjects as they move, it will be a challenge to get the key to be accurate. Lighting will have a strong effect on the shutter speed, so it's important to use enough light to get the correct exposure. The aperture will also define the depth of field. It's important for the depth of field of the subject to match the background. If the subject is partially in focus and fades into being out of focus, and then the background is suddenly in focus and fades to out of focus, it will cause great problems. Again, aperture will be determined by the amount of light needed to get the correct exposure.
The first aspect to creating a good green screen key is to light the subject well. It's a matter of using basic three point lighting to create a good image. The backlight may also be helpful to those who are new to green screen. While a great digital artist can work without a strong backlight, newbies may find it helpful to use either a stronger backlight to differentiate between spill and the actual background or to use the complementary color (in the case of green, that's purple) to offset the subject from the background.
A green screen is a large piece of cloth or a wall painted a specific color of green. After lighting the subject, it is important to light the screen as well. The picture above is an example of bad green screen because the screen changes color. It is important for the screen to appear as even as possible to make the key work. More variance in the screen means turning up the "tolerance" in post-production. Tolerance is a technical term that describes how many steps away from a certain color will be removed in addition to the base color being removed. Spots that are brighter or darker than the specific green being removed may create a situation where the tolerance will have to be turned up so high that it will remove parts of the subject along with the background. Unlike other lighting techniques, there is no reason to add "interest" to the background with light. It should appear as flat as possible.