Some of you have cameras that will accept a separate flash unit. These flash come in many sizes and designs, but the best will allow you to rotate them 360 and angle them up and down. The reason for this is that you can bounce the light from the flash off of ceilings or walls and get a much more natural, soft and diffused light quality than you can ever get with the flash pointing directly at your subject. This is the main downfall with on-camera flash that can only be overcome with a separate flash unit.
The easiest way to use bounce flash is to bounce the flash off the ceiling by pointing it stright up. This will light up the ceiling and create a softer and larger light source from above. This tends to look very natural becuase light from above is what we normally experience indoors and outside.
Another way is to bounce the flash sideways. This can give much more dramatic light quality and can enhance texture.
Either way, it is important to remember that the color of the wall or ceiling you're bouncing off will affect your light color that illuminates your subject, so white walls and ceilings work best, and wood or dark walls and ceilings don't work very well. In the same way, very high celings won't work well either because the amount of light that will bounce back could be so low that you don't get enough expousre.