The Rule of Three
The Rule of Three is a simple concept that can be applied to most aspects of design ranging from architecture to web pages. The rule advocates grouping odd numbers together. The idea is that odd numbers are more memorable and appealing to the eye.
While symmetry is a steadfast design principle, odd numbers create movement and visual interest. They help your eye move across the visual plane.
This can be applied to many details in the design world. In a website, for example, the principle could be applied to a three-column layout or a single typeface with three varying weights to differentiate sections of a page. This uneven grouping also creates a natural hierarchy.
From photography to woodworking, if you find yourself in a visual bind, The Rule of Three can open up a whole new range of creative possibilities.