Just do the things as you doing for Google optimization. There is no any different way of yahoo optimization.
Yahoo is a bit more "tolerant" to keyword density, and the best approach is to use synonyms rather than plain stuffing. This way you fit into both requirements. One of the best tips ever, believe me.
Yahoo results are being powered by Bing - so take that into consideration as Yahoo is little more than "wallpaper" for Bing now. Just keep on working, and you'll be fine IMO.
There's no difference. You just have to do your it as you do for other search engines and you will start ranking well on Yahoo too. You can increase your link popularity and gain ranking benefits on Yahoo search, but also, be careful not to overdo it. As you might start ranking well on Yahoo, but might lose out on Google raking, which is far beneficial than Yahoo ranking.
There are things you can do to optimize specifically for Bing (if you haven't heard there is no Yahoo! search engine anymore - Bing is powering Yahoo! organic results now) by focusing on ranking factors that you know carry more weight in Bing's algorithm. But generally speaking, most people optimize for Google (since they have 65-70% marketshare of search) and let their other rankings fall where they may. If you follow sound optimization techniques and strategies, they will typically work across all engines.
Great... thank you for the update as I was waiting for Bing finally powering Yahoo but wasn't sure when it was going to happen. Many thanks for that. Does anybody know when Yahoo UK will also be powered by Bing? Sorry for hijacking the thread but it will you as well as SEO for google and bing is pretty much the same, although bing (just like yahoo in the past) pays too much attention to keyword in domain name. Also, bing pays less attention to the quality of the content.