9. Thou shalt stay Consistent
Include a standard navigational structure on every page. Though it may mean a serious challenge for the designer, users should only need to click once to find every major section of a site.
Also, this includes using standard link colors in all text links. Blue: hyperlink; Purple: visited hyperlink; Red: active hyperlink.
10. Thou shalt Know Thy Traffic
Use a site-wide statistics program that enables you to determine what brings someone to the site, where they go once they arrive, and when and where they leave.
This critical information helps with marketing efforts as well as identifying parts of the site that need tweaking or adjustment to help you increase sales. If everybody bails from your site at the same page, knowing this can help you change the page so people go from "bail mode" to "buy mode"!