You might think that if you want a dark background in your photos, you need to be shooting with a, well, dark background. However, the beauty of lighting and exposure is that with a proper setup, you can turn even a white wall into a dark background. This helpful video will show you the basics of doing just that.
Coming to you from Beyond Photography, this tutorial gives a practical breakdown of how to make a white background appear dark while still lighting your subject properly. When you're working with artificial light, it's important to divorce how you think of the scene in front of you based on your natural eyesight as opposed to how the scene will be rendered when lit. As Andrew Boey demonstrates, with consideration of your modifiers and light placement (notice how he's very careful not to spill light onto the background) and of your exposure, you can control how lit (or not) your background is. Essentially, he is taking a base exposure that would render the entire scene nearly black, then adding in artificial light at a power appropriate to its placement and the exposure settings to light only the subject. It's a good technique to have an understanding of and will help make your lighting more versatile in general. If you'd like to watch the episode he mentions on rim lights, you can do so here.
Kind of fun but really a simple set-up to understand how to achieve black BG on white wall.
Grid on softbox is also great...
The answer is simple, even without reading an article - UNDEREXPOSE IT!