Since Yahoo is now using Bing's search engine, the factors are the same as for Bing. These are not always the same as the Google factors. visit here:- "http://www.bing.com/community/site_b...d-content.aspx" "http://affiliate-marketing-forums.5s...rank-bing.html"
Generally it does not seem to be very different to Google SEO. Read this article, it stresses the importance of having a good site structure: www (dot) beanstalk-inc (dot) com/articles/seo/seo-for-yahoo (dot) htm
I think we can't separate SEO as Yahoo SEO and Google SEO. Try always effective link building techniques. Then your keyword will get good ranking in major search engines.