Lighting is SUCH a fine art that I dare not give any advice of my own because I am so far removed from being able to advise on this subject I may as well be in Narnia. All I know is that the background must be lit as brightly as possilble and be totally free from shadow.
Here is just one site I found when googling on Chroma Key Lighting, which goes into much more detail. There were of course thousands of other sites.
http://www.studio1productions.com/Ar...maLighting.htm
I'd love to see the result of your chroma key work!