You need to build links for the site in other to get better PR. PR depend on number of BL you have for the site, start building quality and relevant BL for the site... Good luck
I have two website but page rank is 0. How i will increase my pagerank www.infozonebd.com www.chuadangabd.com
Content will not usually help in increasing pr. Pr is based on the number of quality links that you have to your site. The google idea though is that if you have unique content other webmasters will link to your however this is mostly not the case when you are in a competitive market. This might work though for non profit organizations. So yes submit your site to directories.
You need to build backlinks from different sources such as article submission, posting on relevant blogs, social bookmarking sites, and press release distribution.
Adding good content to your site is indispensable. But you have to get some quality links to your website too. Moreover, understand that Page rank and SERPS are not related to each other. If your need to get a good pagerank, get some quality inbound links. Also keep updating the content frequently. Here is how that page rank is calculated: Your website's PageRank = 0.15 + 0.85 * (a "share" of the PageRank of every page that links to it)
My site mrdefinite.com promotes "nofollow", meaning to say you can gain backlinks by commenting there.