Some "golden rules" for your page
View it with more than one browser. Most people will use MS Internet Explorer, but there are others: A standard test should include at least viewing your page with some version of Netscape and Opera.

View the page in different screen resolutions and with different settings for colors. Again: what looks OK on your PC might not look good on another. Things can get especially messed up with different screen resolutions. All of a sudden menus might not fit anymore, or visitors can only see half of the page. The more you try out yourself, the better for your visitors.

Check for broken links on a regular base. It is easy to do and only takes a few minutes with the right tools (see XENU in the tools section).
It does not matter if they are internal or external broken links , they make your page look abandoned and unprofessional, and people tend not to buy from abandoned or unprofessional pages…