Like I have already said, Yahoo covers about the 25% percent of the searches. It is the second major search engine therefore it is worth spending some time to learn a bit more about its algorithm.
Its spider is called Yahoo! Slurp and it works in a similar manner to the Google's one. It is also important to say that the WebRank does not have a relevant importance in the ranking algorithm. WebRank was introduced by Yahoo, following the example of the Google's toolbar PageRank, but it worked collecting data in order to calculate the popularity of the websites not to indicate the rank of a website. And while it is true that often a website which had a high WebRank, it ranks also well, there are several reasons to explain this. The simplest is that if a website has a high WebRank, it is popular; but if a website is popular it means that lots of information can be found, as a result it will be probably made by lots of pages. We saw that the dimension of the website is an influent element in its rank. Anyway the WebRank is no more included in the Yahoo toolbar even if tool with the aim of evaluating it are available online.
There is not a lot of information about the Yahoo's ranking algorithm, in particular compared to the Google's one. Also the official website does not really help, but from some experiment based on searches and the analysis of the results, it is possible to understand the key factors.
First of all, the main element is the keywords. If the Google's algorithm is particularly concerned about the backlinks, the Yahoo's one is more about "on page" factors.
For Yahoo the most important place where a keyword has to be included is the title. This is fundamental, it looks very hard to rank well if the search term is not on the title of the page. On the other hand, it is not necessary that the keyword is repeated more times.
The second more important place for a keyword is the filename or the directory where it is stored.
Then it is also important that the keyword is in the domain name, and possibly it is not a derivative from another world. Hence "www.potbellied_people.com" is not as good as "www.pot.com" for the search term "pot" even if it is better than "www.belly.com".
The keyword has to present with a high density also in the content. Here to achieve a great result with Yahoo, you may risk to be punished for keywords stuffing by Google. In fact a density above 7% can be good for the former and bad for the latter.
Since Yahoo trusts very much its own directory where the website are inserted in relevant categories by human employees, it is a great boost to your rank having your website in the Yahoo directory under a category which is relevant to the search terms. This is more than just an important backlink for your website, like in Google.
Then it is relevant the PageRank. It looks that the weight to the links is mainly given through the importance that the PageRank has in the algorithm. It is less important than having a keyword in the filename or in the title but it does a part.