to get a good black background you don't want any light falling on a dark backdrop (should not need to be black) to make sure no light gets on the backdrop it should be as far away from your sets as possible (so the bigger the backdrop the better) and you should only have as few light on the set, and all other lights off. If the background is far away it will be out of focus which should smooth the flaws in in, and if no light it touching it it should look black as long as it is a dark color. On problem is the light walls in most houses may reflect light onto it if you have a lot of lights on.