Submitting your site to Yahoo directory is pretty simple since the collaboration with Bing search engine. So you basically just have to do it one time in Bing Web Master Tools for both search engines.
You must have a Microsoft Account to do this and signing up is free. Sign up for your Bing Web Masters Account
You will be taken to your Bing Web Masters account dashboard.
Add & Verify your website with Bing
Enter the URL of your site into the Add a Site input box and clicking Add a Site.
Verify your site
There are options with steps to take in verifying your site. I prefer Option 2 if using an SEO program however Option one is permanent on your hosting.
Click the verifying option best suited for your site and follow the on-screen instructions:
Once you have added the ownership verification code to your site click Verify.
If everything is good to go you will see a green message verifying your site. If something is wrong a red message will appear and you can try and submit your site again.
Add your sitemap
Sitemaps are a great way to tell Bing about your site structure, pages, etc.
Enter in the URL of your sitemap and Submit. This will be pending until Bing crawls your sitemap to your site.
Now you are done.
Bing crawls URLs submitted about every other week. So dont panic if you dont see immediate changes and indexing right away. I always tell people to check their search engines stats at 30 days, make any adjustments on your site then give it another 30 days. you should see higher results, it just takes time for the search engines to do their job.
If you need a screen shot of these steps you can check out the Getting Started with Bing Web Masters.