If you are getting good result in Google then do not think for any other search engines because almost 80% traffic comes from Google, just concentrate on link building and update contents regularly..
Generally we use google for any searches and also any sites which we like. So use yahoo for any searches so as per yahoo your site ranking will increase for yahoo search engine and method of both search engine is same for ranking.
I went to Yahoo SEO page before and I noticed the usage and the UI is not as user-friendly as Google. What do you think? The very first step already pull me down to have SEO with Yahoo! but I think I'll give it a try again.
Try to being ranking in google then the site automatically ranked in yahoo and doing SEO properly......