There are many versions of Web Design Rules. They are from different point of views. But, I have my own version.
The purpose of my Top Five Web Design Rules is to maximize Web Site usability.
Easy to read
Think about the audience, they using variety computers, monitors, Internet connections. They may have difficult to read tiny letter, color blind.
Text size, image size and paragraph organization.
Easy to navigate
It means the target audience of your site should know where they are at all times when they visit your Web Site. If they get lost, they are able to go to home page, a site search, or a category list from any page on your site to determine: 1) where they are, 2) where they might want to go, and 3) where they have been.