How to Create Dark Background in your Photos
On this video photographer Mark Wallace from AdoramaTV talks about how to take advantage of the inverse square law in order to knock out a background and make it appear completely dark. By comparing distances of your light and model you can achieve a solid black background in even the messiest location.
Here is the Inverse Square Law episode for anybody who would like some more in-depth info
You can watch many more photography tips on the LensVid technique section.