Different Search engines focus on different factors to rank Search result according to algorithms. However these factors have biggest impact on SERP.
Site Speed and accessibility
You may have unique content, more traffic and social engagement .But if your site is not properly access, index or crawl by search engine it give zero impact on SEO. So websites need to be easily accessible for both search engine and as well as audience.
According to Google site speed has less impact nearly 1% in the ranking however every users want fast and responsive sites. pages with longer loading time tend to have higher bounce rate and lower conversion rate which impact on the ranking. In addition, slow page speed means search engine crawl less pages in allocated crawl time which may have negative impact in Indexation of web pages. So to achieve good rank websites need have high speed time as well as accessible for search engine as well as Users.
Mobile Friendliness
On April 21, 2015 google release a new mobile friendly ranking algorithms which boost the mobile friendly site in google search page result. So every site need to mobile friendly. Since more search are performed from mobile in many different country then every webmaster, SEOs and content marketer need to think about it for mobile optimized sites. To optimize the site for mobile users we need to a focus on page speed, site design, mobile site configurations, use of flash pop-ups, and many more.
Keyword Research
Keyword is search term or phrases that help to find website through search engine. keyword research is important in prospect of SEO, for keyword analysis different tools are available. Using available tools we can analyse the required keywords with their Search volume and competition. Depending on the purpose of the web pages/sites we can choose keywords suitable for us. However the placement and density of keywords used also matter on the SERP, Keyword stuffing may have negative impaxt on rank so we need to choose best keyword and their placement in the Content of web pages .
Link Bulding
Link building has biggest impact in SEO, However quality and relevancy of Link may differ the ranking of sites. Link coming from trusted or high page Ranked site and relevant or similar purpose sites improves the rank of our site so we need to connect with trusted and relevant site during link building. Bad link and broken link effect on the ranking of sites so we need to avoid these type of links in oue sites.
Social Media
Social media is one important factors in SEO nowadays. Every site owner focus on the promotion of their site through social media which is also called Social Media Marketing (SMM). When people engaged in Social media which effects on the traffic of Site so people spend time and money for SMM. Facebook, Twitter, instagram, Google Plus are the popular social media however there are huge number of social media sites. Every sites use social media icon and social media sharing options in their sites to increase the social media engagement.