Let's start with something well known: generally a good website is that with competitive keywords, with good content and quality links. To make the search engines' spider visit your site all the time you should make updates permanently, it's a big mistake to let the same articles for a long time. Yes, sometimes it may be hard but there are some tips, of course.
You can build your site as a blog, or a place where people come and chat on a subject related to your site. This way let's say you will have permanently changes on your site, and SE's will crawl in.
Although you can improve your site with a content rich in keywords relevant.
The RSS feed is another important topic to consider when discuss about ranking on Yahoo. You can create one by yourself or use some specialized softwares. Then you should add the RSS file in MyYahoo page; if never utilized it it's time to create one. Yahoo's spider loves more the site he finds by RSS than those submitted in directories; so you should have an advantage with this.