The rule of thirds is a powerful technique for composing interesting and dynamic photos. Learning this compositional technique improved my photos as much as anything I have learned.
To use the Rule of Thirds, divide the viewfinder frame into thirds, both horizontally and vertically. That is, imagine two equidistant up-and-down (vertical) lines and two equidistant side-to-side (horizontal) lines. Like a tic-tac-toe board. On some cameras, you can actually have the tic-tac-toe board show in your viewfinder.
Then, compose your photo by placing your subject at (or near) one of the four intersecting points . . .
. . . and/or along the lines.
The Rule of Thirds is a good guide for placing the horizon. Place it on one of the two horizontal lines. If the most important or dramatic part of your shot is the sky, then place the horizon on the lower horizontal line, leaving 2/3 of the frame for the sky. On the other hand, if the foreground is the most important part of your photo, place the horizon on the higher horizontal line.
In this photograph of a dock on a small lake I tried to place the subject — the dock — on or near the upper right intersecting point . . .
In this photograph of a sunrise sky, I placed the horizon on the lower horizontal line so that most of the photo would be the beautiful golden sky . . .
(Click on the photos for the full effect.)
By the way, this principle works whether you are shooting with your camera vertical (which photographers call portrait mode) or horizontal (which, to photographers, is landscape mode).