Directories serve two purposes in your web development efforts. One, a link from a directory is counted as a back link and hence increases your link popularity. Two, some directories will send you targeted traffic.

Webmasters who use directories for increasing link popularity should check out the directory first to see if the directory is SE friendly or not as, only a SE friendly directory will give value for their links.

So, how do you detect a SE friendly directory? Here are some tips, which will help you do so.

1) Check the url format of the directory. Some directories have urls in the format http://sitename//index.php?id=1&c=10... for their category pages. This is called a dynamic link and search engines find it difficult to crawl such pages.

Urls for the category pages should be in a static format. Example : http://www.indexbizz.com/cat1.html . Search engines ccan easily crawl such pages and your link will also get crawled.

2) Your link should not be a JavaScript link. Some directories use JavaScript to jump to your site from their category pages. Search engines find it difficult to crawl such links.

3) The directory must not ban search engine robots from crawling the category pages. You can check whether such a condition exists or not by looking at the robots.txt file of the directory. This file is located at the root level of the directory. To see this file just type robots.txt after the domain name of the directory. Find out what this file is saying, for example -

User-agent: *

Disallow:
This will allow all SE bots to all the folders and files in the directory.

User-agent: *

Disallow: /
This will keep all SE bots away from all files/ folders in the directory.

User-agent: *

Disallow: /mydirectory/
This will keep away all SE bots from crawling the 'mydirectory' directory and all files under it.

So be wise in your selection of SE friendly directories, and put your efforts towards getting links from such directories that fulfill the above conditions.