EVERYTHING YOU NEED TO KNOW ABOUT FLASH
Blend the light
Make flash complement the ambient lighting
In many cases, flash is at its most effective when the viewer is unable to tell whether it was used. With care, it is possible to integrate the light from your flash so seamlessly that it is not easy to identify which source is dominant. This technique is popular because it is capable of producing seemingly ‘impossible’ lighting, where the subject and environment are illuminated so it appears natural, but the distribution of shadows and highlights is such that detail is perfectly controlled, which is unlikely if only natural light is present.