Off page, SEO is basically your advanced Backlink building strategy. If your site has no incoming links from other websites, your site will not be included in search engine indexes.
The best backlinks are those that come naturally as a result of great content. Your website must contain high quality, useful, timely content that people will actually want to link to. This occurs when a user links to your page on their blog, on their social network or on a social bookmarking site. Such links are considered passive and you cannot control how people react to your content, but you can tailor it to meet demands and to raise interest. These, however, are not the only links
you should consider. There are many possible ways to generate links.