unique and interesting content is the most and primary factor that attrcats more visitors and traffic.
Hopefully your Pagerank is N/A and not a big fat ZERO. If it's Pagerank 0 (N/A) it's still not calculated yet, because the site is new, new domain or under heavy restructure. It will come in time. Build up quality unique content and pages, get high pagerank 'dofollow' backlinks to site, and use whitehat SEO. Navigation should be less than 2/3 clicks to get to every page, a sitemap.xml is helpful for search engines on larger sites. Mostly google bases pagerank on how it and others trust you for a good quality site. It will take a lot of time before its next update. Work on your site for customers first then SEO friendly. If you have a Pagerank 0 and it's actually a ZERO, then your site has been blacklisted or sandboxed by google and can be even de-indexed. Go to Google/Webmasters and resolve the issue and request a resubmition when fixed. Avoid keyword stuff, linking to bad neighbourhoods, malware, blackhat SEO, etc. Avoid link farms which contain 1000s of links on one page, etc.