Thanks to the laws of physics, it turns out that brightness diminishes with the square of the distance. If you position a light 5 feet away from your subject and then you move it to 10 feet, the subject will only receive a quarter of the light that it had at 5 feet.

In photography terms, that's a two-stop reduction in exposure. That means you can radically change the light on your subject by moving a table lamp closer or farther from your subject, for instance.

If you paid attention to the last tip, you can probably guess where this is going: Your camera's flash has essentially no effect on the background, assuming that the background is a fair distance away from the subject. Suppose that you're taking a photo outdoors. You can move your lighting closer or farther to change the relative exposure of the subject, but the background will expose the same either way as long as you keep everything else the same. That's liberating, because it means you can fiddle with your flash's position and settings without worrying about what's going on behind the subject.

It should also go without saying that this also means you'll never illuminate a distant background with your camera flash.