If you’re shooting in a dark room where natural light isn’t an option, then you’ll need to use flash. It helps to bounce the flash light against the ceiling or a wall for an even exposure. If bouncing the flash isn’t possible either, say due to high ceilings, then you’ll still need to diffuse the flash, otherwise it will look too harsh. Try using a flash diffuser, the diffuser part of a reflector or shooting with the flash off-camera (or combine all three!).