What makes for a good photograph?
There are three key elements to a good picture - light, subject and composition. Great photographs are in focus, sharp, have good exposure (light) and composition.  In order to take the perfect photograph you must be at the correct focal length, set the appropriate aperture for the subject(s) in your frame, make sure the shutter speed is set for the action you are capturing (higher shutter speed for sports, lower shutter speed for portraits) and make sure the ISO is correctly set to work with both the shutter speed and aperture.  Understanding how the ISO, Aperture and shutter speed work together is key to taking the perfect picture.