After Google Penguin upadates...do High PR Directory Submissions only, because Low and Zero PR sites are not worthyless, and waste of work..which leads to penalized by Google...So be aware with these type of websites...
As we have to do natural link building so we need to use both high pr and low pr.. we also have to use other methods of link building so that it would look natural to search engine.
High pr directory submission is a marketing strategy that has proven very effective. Just to add a site through high pr directory submission which greatly increases the exposure and the site Page Rank. This is because when you send the name of your site, it will be accompanied by your URL, which means that you are getting a link to you. You need inbound links to increase your Page Rank as it is a decisive factor when it comes to search engine Web sites indexing.
As we need natural links so we have to use low pr and high pr sites so that it would look natural to Google search engine.
Also, only directory submission may not work, you have to use other methods of link building too.