There are 3 major factors to consider for your SEO campaign: keyword analysis, on-page optimization, and arguably the most important, back-links or inbound links.  Before back-links used to just be a referral source that could generate some unexpected traffic.  From my experience they are now the most weighted factor when it comes to Search Engine Rankings. In case you are unfamiliar with the term back links, simply put, back links are links to your site from another site.