Yahoo is one of the most important and major directories on the web. Yahoo is divided in the main (original) Yahoo, the international Yahoo sites, and the regional (city) Yahoo sites. As of March 2004, Yahoo no longer shows Google’s results. Instead they use their own crawler, Slurp! Directory results are no longer shown mixed with web results. We recommend you pay the yearly $299.00 site subscription only if you have an advertising budget that can handle this. Most people use the default search with web results although an inclusion in the directory does help you gain Link Popularity!
On the bottom of the Yahoo front page you see a Link, How to suggest a site.
There you can see it’s possible to get into Yahoo in four ways:

Site Match™

- Guaranteed inclusion in Yahoo! Search and partner sites
- Frequent refresh every 24 hours
- Reporting to track and optimize performance
- Site review to ensure relevance and help high quality sites perform better

Pay-For-Performance™

- Keyword-based advertising with guaranteed placement on Yahoo! and partner sites.

Free URL submission

- Suggest your site for inclusion in Yahoo! Search (requires registration).

Yahoo! Directory

- Suggest your site for inclusion in the Yahoo! Directory. One English language listing in Yahoo! will show up in US Yahoo!, asia.Yahoo.com, sg.Yahoo.com, au.Yahoo.com, ca.Yahoo.com, in.Yahoo.com and uk.Yahoo.com.

Next we look at how to get into the major directory. We describe how to get into the free search engine at the search engine page about Yahoo.

How to get into the Yahoo directory?

There are two ways to get listed in the Yahoo directory, the free way for non-commercial sites and the paid way for commercial sites. To get a listing in the Shopping & Services or Business to Business sections (either main or regional) of Yahoo, you now must use Yahoo's "Express" submission option.
Moreover, your site must be in English or of an English section to be listed. When you want a language specific site listed go to one of regional Yahoos or scroll down the world section to find your appropriate local country section.
Simulate the search your clients would make when looking for your site on Yahoo’s directory. On the top left side, notice the “suggest a site button”. If you don’t see this, scroll down the categories. When hitting the “suggest a site button” you see immediately if you can submit your site for a free review or if you must pay for a review.

Tips on good ranking in Yahoo

1. In each category, Yahoo currently lists sites alphabetically by TITLE.
2. Unless your site name has an alphabetical advantage, choose a category that displays your important keywords in the name and that has as few other entries as possible.
3. Try to ensure that your most important keywords appear in the title, description or URL.

First, in each category, Yahoo currently lists sites alphabetically by TITLE.

So if you can come up with a plausible title for your site that starts with a number or the letter A, B or C, go for it. Note that if you are running a business, Yahoo asks that you use your actual business name (or your "doing business as" name) as your title. Some Yahoo categories now have "most popular" sites that are listed first, but at least initially it will be almost impossible for you to get into one of those slots, so alphabetically high is your best bet. Note however that most people find things on Yahoo by searching, not by scrolling through the categories, so it isn't the end of the world if your company name happens to be "Zztop, corporate".

Second, as noted above, unless your site name is well-placed alphabetically, choose a category that displays your important keywords in the name and that has as few other entries as possible.

Ask yourself, "Will my site be visible on an average browser window without scrolling?" If at all possible, you want to be. Don't be upset if you can't achieve this; it is an advantage, but it's a minor one. More important is the keyword in the category name.

Third, try to ensure that your most important keywords appear in the title, description or URL.

Work them into the text in a natural way. A list of keywords isn't acceptable! Because your Title will often get edited, make sure the really crucial keywords are in your Description. If your Domain name has your major keywords in it, even better, because your URL can’t be edited! However, don't go overboard stuffing keywords. You want something that reads well and is descriptive. The order of importance of your keyword is first the title, next the description and finally, the Category.
More in-depth tips for major directory Yahoo rankings inside your SEO Effect!