The Four Basic Principles

1) Contrast - avoid elements on the page that are merely similar. If they are not the same, then make them very different. (often the most important visual attraction on a page. (Main reason to grab people's attention). 

2) Repetition - Repeat visual elements of the design. It develops the organization and makes the page more united. 

3) Alignment - Every element on the page should have visual connection with one another. This makes the page clean, sophisticated and have a fresh look. 

4) Proximity - items, which are related together, should be grouped together. This makes the page one whole unit rather than separate units. This also makes the page clean and organized.