You can try this as well.
Put up a white sheet or something white as long as it's translucent enough to allow light to shine through. Place as many lights as possible behind this white sheet. Make sure they're all the same like all tungsten or all flourescent and the same color temperature.
Now put your camera on a tripod in front of this sheet. Put your camera in manual mode. Set your f/stop to 11 (number I pulled out of a hat). Figure out what shutter speed your camera wants you to use to get a nicely exposed picture of the sheet. Take the picture. You're sheet will probably be a bit yellow or grey.
Now decrease the shutter speed or rather make the shutter stay open longer. So if the shutter speed was originally 1/250 then you want it to be 1/200. Keep doing this until you get a nice blown out sheet.
This will tell you the exposure you need to get a nice white background.
Put your model in front of the sheet. I'd have them stand about 6 ft in front if possible. Take a picture. If you see the light bleeding onto the model then increase your f/stop. So we started with f/11 then we'd want to take it up to f/16? We do this because the shutter speed controls how well your background is exposed and the f/stop controls how well your model is exposed. Since we want less light on the model then we make the aperture smaller by increasing the f/stop.
Take another picture to see if you're getting the effect you're looking for. You need to make sure the model holds very still if you have a slow shutter speed.
Good luck and let us know how it goes.
