The smart people at SearchMetrics created a report about the most effective SEO rankings of 2014.
Summary of Findings
Content remains important. Good quality, relevant content ranks better (on average). This content includes occurrence of related terms in context, high word-count and media enrichment (pictures, videos, etc).
This refers to the technical performance of a page. Well optimized pages contribute to good rankings. This includes – good site architecture with optimal internal linking structure, short loading times and presence of meta tags.
Quantity and quality of backlinks remains crucial. Strive to build natural, relevant links that point to your website.
Social media is not a significant source of rankings (compared to other factors). However, posting quality content to increase engagement (+1, Likes, etc) still influences rankings.
User signals refer to higher click-through rates, lower bounce rates and a high time-on-site. They all seem to have an effect on SEO rankings.