Rule of Thirds

Definition: The rule of thirds states than an image is most pleasing when its subjects or regions are composed along imaginary lines which divide the image into thirds — both vertically and horizontally. Like a tic-tac-toe board! 

This picture of a cute puppy is a good example! The right vertical line would pass straight through him!

This log would be a bad example =( because no points or lines would touch it. 

Disclaimer: The first picture is not mine. I borrowed it for educational purposes.