A flash is used in photography for two main reasons: to act as the main light source when the surrounding light levels are low, and to fill in shadows by adding a little light to balance an already strong light source such as the sun. An on-camera flash is not particularly good at either role, as it is very close to the lens and tends to reflect back from the retina of the subject’s eyes, producing the red-eye look. Separate flash units are much more useful for flash photography.
Attach the flash gun to the camera, but don't aim it directly at the subject. Instead point the flash head at the ceiling or a light-colored wall adjacent to the subject, or against a white card in the room. This bounces the light off of a large surface onto the subject, giving softer shadows and a pleasing illumination for portraits.
Off-camera flash prevents red eye and adds drama.Connect the flash to the camera using either the provided cable, wireless or infra-red trigger. Hold the flash off to one side and slightly higher than the subject while the picture is taken. Have an assistant hold a white card to the other side of the subject's face to provide some illumination. This gives a pleasing dramatic lighting effect.
Place the subject between yourself and the sun so that the sun is highlighting her hair. Place the flash gun alongside the camera and, using the exposure controls on the flash gun, reduce the power of the flash gun to half power. Take a test image and make sure that the face is nicely lit by the flash while the background and sunlit hair are still properly exposed. Adjust the exposure on the camera until you get the image just right.
Place a diffusing white umbrella in front of the flash gun between the flash and the subject. The thin white cloth provides a very large diffuse light source that can give almost shadowless lighting when close to the subject and pleasing, light shadows when further away.