3. Black Background: To get a beautiful black background, always use a flash while setting the camera at small aperture and high shutter speed. Depending on the external light available, vary the aperture and shutter so that very less background light reaching your sensors. Alternately, you can use a black cloth or background while taking the snap - ensure that the light from the flash doesn't reach the cloth/paper. Use a bounce flash to get diffused/smooth lighting on the flower. Here is an example.