put your horizon line either at the top third of your photo or the bottom third. How do you know which one to use? If the sky is interesting with lots of clouds, put the horizon line at the bottom, so you see more sky. If you’ve got a boring, cloudless sky, put the horizon line at the top third, so you see more foreground instead. It’s as simple as that. Just remember; there’s a reason they call it “dead” center.
