White, flat objects bounce pure, white light back at your camera lens. This can be a wall, a sheet, curtains, or any object that is white and flat. Since you won’t be able to move your flash to bounce it off of certain objects, you will need to make sure there is a nice, white object behind your subject to bounce your built-in flash off of.
Position your subject right in front of the white object so that you don’t loose any power from the flash and adjust your white balance. This will insure that you get the best shot.