NEX7 w/ 50mm - smoke
I have a black backdrop (you can see the cloth outline bleeding through the smoke a little)....
On the right side, I have a continuous LED light (200 lumens) shining from the back end ensuring the light doesn't hit my backdrop. I then have a wireless flash sitting on the left side laid down on its side, so you'll have more of an upwards angle. The flash again is sitting to try to prevent leaked light from hitting the background.
The continuous light on the right side could probably be replaced with a bounce reflector or another wireless flash. I just wanted to ensure the smoke was fully lit and the led light was the best I had to work with.