Christian Zimmermann's Principles of Good Web Site Design

Have original content: That seems pretty basic, but people will only come again if there is actually something to learn from the site...
Keep it up to date: Broken links, inaccurate material and outdated texts obviously do not encourage people to come back.
Do not use graphics if you can do it with text: A third of internet users turn graphics off (or have a non graphical browser). Additionnally, all text that is in graphics will not be interpreted by search engines. And graphics just make the page download longer.
Avoid tables: They make it messy on some browsers, and search engines get confused.
Do not hardcode the layout: Not everybody has the same screen or window size as you, let the client software (the reader's browser) organize the layout for his viewing pleasure. This means in particular, do not force font or change the color of the text (imagine a browser with a white default background and you force a white text...)
"This site is designed for any browser": Why limit the potential readers to those of a specific browser? Imagine a new TV channel viewable only with a certain brand of TV sets.
Have stable addresses: How are people going to link to files or your site if they keep changing? And imagine the frustration of those droping in from a search engine only to find something different from what they expected.
Have transparent HTML coding: There is less risk for the browser to be confused, and files get much shorter.
Do not use Java or Javascript: It just gives additional opportunities to make scripting errors. If the functionality of your site depends on it, many people will not be able to navigate it, either because the browser freezes, or because they have turned Java and Javascript off.
Avoid frames: Unless you really know what you are doing, do not use frames. The most common mistakes are: sites not navigable without frames, hardcoded frame sizes make that certain areas spill out of the window and cannot be reached, and windows too small to be readable.
Do not use plug-ins for critical fonctions: There are just too many sites that I cannot access because they require the latest version of a plug-in. And why have people waiting for huge files to download if all they want is to get past that first page...

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