I know your question is specifically about Yahoo but you have to figure Google into any equation when you are talking about SEO. It doesn't really matter what engine you use or like best, Google is king of the mountain on this one and if you ignore it, your site will never see the light of day as far as ranking goes.
Having said that, the control of search engine optimization is ultimately Google, simply because their technology far surpasses Bing and Yahoo. (sorry yahoo and Bing but it's true)
Optimizing so the search engines will spider you site involves a number of tasks. First, you need to know what the engines like and do not like. One thing they like is blogs and they especially love WordPress blogs. That doesn't mean that the site has to be hosted on WordPress but a theme obtained from WordPress is very search engine friendly. There are also WP plug ins that increase the visibility of the site. WordPress ia basically a format of a content management system that search engines like.
There are also some basic rules to follow. Unique, original content is needed and it needs to be updated frequently or it will start lowering rankings. This means you cannot post articles from other sites or have a spinner scramble and rewrite articles and post them as your own. Google is v ery sophisticated at ferreting sites that do this out and they shut them down very quickly. And speaking of articles, writing and posting articles in online article ezines and directories is also critical for SEO, regardless of the kind of site you have.
Another thing to do is to make sure that the site is very user friendly and ways to do this is to run a usability test. There are many online tools to do this and sites that do this on a limited basis for free and a more extensive basis for a fee. Another thing to make sure of is that the site is easily navigable, with clear menus, links, etc. A word about ease of navigation: Google does not like flask links in the menu or flash navigation bars. Putting flash in other areas of the page is fine but the spiders don't recognize sites with flash nav bars and links as even being a web site so it is likely they won't even crawl it, so your site would not be listed by any of the search engines.
Another thing to pay attention to is back-links. There should be back-links to your site and the more, the better, but they must be from legitimate sources of traffic. One way to accomplish this is to comment on other blogs or sites in the same area of interest as the site you are optimizing , and leave a relevant comment to the post or site, and include a link to your site in your signature. You must not spam a site in order to get back-links as you will get shut down before you can blink.
Opening a page for the site in a number of social media sites such as Facebook, Stumble Upon Myspace, etc is also advisable. This is another way to get back-links.
There are many ways to optimize a site, but these are a few of the basic essentials.
Hope this helps.
Experience as marketer and owner of Dream Quest Marketing