Rule of Thirds
Rule of Thirds is one of the guiding principals in photography and is super simple!
Basically, you want to think that your image is divided into thirds, both horizontally and vertically, like the grid below.
The theory is that if you put your subject or points of interest along the lines or where the point intersect, the viewer will interact with your image more naturally.
I think it makes images look more interesting and also somehow tells more of a story than if your subject is dead center. Here are some examples of images using Rule of Thirds!