iPhone 5S camera focus
Blurry photos occur because:


skin oil or other cruft (pocket lint) is on the lens
the camera software is focusing on distant objects (when you want a closeup,) or focusing on close objects (when you want a distant object.)


If you are having trouble focusing, tap in the yellow focus box on the screen. You will notice that the software shows a larger yellow box when it detects a closeup shot, and a smaller box when it detects a distance shot.