Not all search engine optimization is keyword
research and link building.
The technical aspects of your website, from the structure of your content, down to the cold hard code, are as important, or even more important, than building links and keyword optimization. If your site isnt search engine friendly, or doesnt adhere to Googles Webmaster Guidelines, then it will be continually penalized, and will never rank to its full potential.
According to Mozs 2015 Ranking Factors Study, these are the top 10 technical SEO ranking factors in order of importance.