* Hiding text using similar colors and background colors can actually be worse than using the same colors.
* If you sell links, Matt says you should use link condoms [rel="nofollow"]. Otherwise your reputation may fall. I assume this means they will devalue your outbound links.
* Assign unique, descriptive title tag and headings to every page.
* Use user-friendly URLs like "african-elephants.html," and not "343432ffsdfsdfdfasffgddddd.html." Don't overdo it either — african-elephants-and-their-habitats-etc-etc-etc-etc.html.
* Minimize the number of URL parameters — 1-2 parameters if possible.
If you think a little, it makes sense: all these tips improve the user experience. Hidden text is not visible to the user, so the page would not be relevant to the search result. The title and the URL are also an indication of the page content. Redirections slow down loading of a page. So if you don't know what to choose in a situation, think what your visitors would choose.
* SEO = optimizing a web page to rank well in search engines