Good SEO depends on good principals that when followed correctly will tell any search engine what a site is about. HTML sets a presendence by allowing a website to communicate properly with a search engine through the use of url, title, headings, keywords, description, and content. If all of these are optimized, you do not need to focus on only optimizing for one search engine because they all read the same data. If you optimize specifically for Yahoo, you may hurt your optimization efforts for Google for example. The best way to do it is to practice good organic SEO with proper keyword research, then access each search engine’s webmaster tools. This will allow you to add a site map, links, etc. Optimize for search engines this way, rather than editing your onsite codes to gain favorability with a specific one. Since search engines have a lot of competitive secrecy and they change their algorithm regularly, optimizing for a specific search engine is like shooting blindly, what works today may not work tomorrow.