Readability/Useability and Design (Mobile Friendliness) Your site should contain type that when viewed in different resolutions and devices is big enough to read easily; buttons and navigation that convert to a specially designed version for mobile devices; and an overall responsive design.
Page speed has to be fast. All other things being equal, the site that loads the fastest will outrank a competing site. Best speeds are 2 seconds or less. Bottom line – Google has allocated a specific time for crawling your website. Only those pages indexed in that period of time will appear in the search engine. If your site is very large, you may have difficulties getting the pages you want indexed.
Page Content High quality content must be found on your pages, especially your homepage. Writing well thought out page content is the single most important thing to getting indexed. If your pages contain useful information, their content will attract many visitors who will post your page in the social media or link it to their website. In creating a helpful, information-rich site, writing pages that clearly and accurately describe your topic is important. Finding the words the users type to find your pages and including those words on your site is important. Careful planning before your site gets to the design phase is imperative.
Social Results Google has formed alliances with social media so far Twitter and Facebook and they still have their own Google+. No matter what others may say about Google +, it is still getting indexed in Google. I am not sure if it is in real time, but it is listed within a couple of days of posting. Twitter results are supposed to be indexed in real time. I have not experienced any real time indexing as yet.
Click stream data from outside the search engines Links from your social media sites to your website. Links from Ads to your website, retweets, pins, etc will enhance your rankings.
User behavior Users will effect your rankings soon. Click-through rates, engagement, time on page, information, shares, links, fulfilling the searchers expectations, all important in greating a good ranking.
Security Late in 2014 and early in 2015 Google asked for all sites to have SSLs. The sites that have a SSL will rank higher than other sites of the same type. This request seems to still be in place because it is safer for the Googlebot when it is crawling your site to be on a secure site/server.