This list of 43 web design mistakes to avoid is very good.. a strong recommended read.
Of the rules, I disagree somewhat with these – so let me ruffle it a bit.
27. Do not use FrontPage…
>> Okay.. I don’t use it for site development anymore, but for some customers it’s a perfect way to make sure they can update their own sites, especially if they’re used to Microsoft Tools. But now, with Apache support for Frontpage Extensions cancelled, there are plenty of good reasons to look elsewhere. If you plan to avoid Frontpage, make sure your clients can update their sites easily using another tool, such as a nice Content Management System that is search engine friendly. I think that Frontpage has been an important part of managing websites for many people, and in the hands of a good developer it produces usable code. The problem comes when people paste in Microsoft Office documents. Then things get awful.
34. Do not use animated GIFs:
>> if Animated GIFs are properly optimized, and palette-reduced, they can be highly effective and efficient way to introduce simple animation and emphasis into graphic elements on a page without the overhead of Flash. Clearly these are meant for limited-pallette solid-color graphics or text – but I wouldn’t list this as a rule. Trouble is that most people do not properly optimize a GIF file. There are some really good programs for this, including some inexpensive shareware. I use Imageready from Adobe for this purpose. If you’ve made the move to Adobe Photoshop CS3, you’ll probably like this post about Imageready Features.
40. Avoid long pages:
>> Have to disagree with this one as a “rule.” The research from work I’ve been involved in shows that for some products and services, long-form pages can convert better than short form. Clearly this doesn’t apply to all pages, and the content itself has to be good enough to warrant continued reading. So perhaps the rule should say “Avoid long boring pages.” Sometimes, having a long-form page is the perfect way to lead the customer forward on their information quest. But the style and writing are everything.