The guiding principle for effective websites is, after excellent content, usability—that is, making the content easily accessible to the users. Usability is a higher priority than everything else, including looks.
This document outlines the usability principles that we recommend for governing your site presentation. These principles are starting points and guidelines. The point is not that you should never deviate from them, but that if you do, you need to do so purposefully. We recommend that no proposed deviations should be undertaken except for those that can be shown to improve usability and design, or which are necessitated due to technology or prioritization when one principle requires the trade-off of another principle.
As a result of these usability standards, users will always know where they are, will be able to get from one place to another quickly, and will be able to find what they are looking for (and many related things they weren’t originally looking for, but are glad to know about).