First thing shooting with any studio lights is don't depend on the camera's metering. Get an inexpensive meter like sekonic 358 and your shots will start to get better. White balance is more important with balack on black so do a custom white balance. I use an expodisc but many people just use an 18% grey card. Another thing is if you can get a hair light or a light on the background for a little more seperation. that will help also.

Tom