Directory submissions are most effective way of getting backlinks. In the internet there are tons of directories available which offer to index your site totally free. Many full paid or partially paid directories are also available. Open directory project ‘DMOZ’ gives the high quality backlink. Paid yahoo directory also give strong backlink.
Directory submission is necessary but no need to waste time with low pagerank directories. Many directories have high pagerank but in which page they index sites don’t have high pagerank. Before submitting , you should test the pagerank of the linking pages by using google toolbar or any other tool. If you find high pagerank , then submit on this page, otherwise not. In maximum cases you should have to give reciprocal links to the directory. They will index your site after seeing their links on your page. You can also submit your site to several low quality directories which indexes sites without reciprocal link.
High quality directories will need several days to review your site. In case of DMOZ it may take several weeks to several months. They are very careful about the quality of site. But links from DMOZ are very effective to increase search engine rankings.
In many directory sites there is a community page also available. Bloggers can interact with each other and able to increase their traffic.