Before you re-design your website stop and think!. A structured and analytical approach to your SEO is essential for a successful re-design. I will outline some common mistakes made by designers when re-designing a website that are not SEO friendly.
1) They sometimes change the domain when they don't need to. By default a website that has been around for a number of years gains trust by search engines. This means that a website with a new URL will go back to the end of the queue. They will have to begin the process of submitting site maps and familiarising the search engines with the website pages and URLs all over again.
2) Replacing text rich sites with Flash websites. This is an all too common occurrence and leaves the website owner wondering why their website if falling off the search engine radar. Flash websites are invisible to search engines like Google and generally only contain a single URL. This is not good for the SEO of their website and can cause problems for websites trying to climb the search engine ladder.
3) Problems with Content Management Systems URLs. With the popularity of Wordpress and Joomla comes the problem of non-SEO friendly URLs. Always remember to enable search engine friendly URLs. URLs should contain keywords instead of characters that do not read well or reflect the page content.
4) Sometimes all the old content is dumped. This can be a mistake as there can be internal links on these pages and also external sites linking to these pages from other websites. Instead of dumping all of the old content, articles can be archived.