2) Images in text: Having a text-only site is so boring but having many images and no text is a SEO sin. Always provide in the <alt> tag a meaningful description of an image but don’t stuff it with keywords or irrelevant information.
3) Podcasts and videos: Podcasts and videos are becoming more and more popular but as with all non-textual goodies, search engines can’t read them, so if you don’t have the tapescript of the podcast or the video, it is as if the podcast or movie is not there because it will not be indexed by search engines.
4) Images instead of text links: Using images instead of text links is bad, especially when you don’t fill in the <alt> tag. But even if you fill in the <alt> tag, it is not the same as having a bold, underlined, 16-pt. link, so use images for navigation only if this is really vital for the graphic layout of your site.
5) Frames: Frames are very, very bad for SEO. Avoid using them unless really necessary.
6) Flash: Spiders don’t index the content of Flash movies, so if you use Flash on your site, don’t forget to give it an alternative textual description.
7) A Flash home page: Fortunately this epidemic disease seems to have come to an end. Having a Flash home page (and sometimes whole sections of your site) and no HTML version, is SEO suicide. Avoid Flash!