There many factors that Google considers while ranking and they are known as ranking factors.
Some of the ranking factors that one needs to know are:
On-Page factors (Keyword in title tag, keyword in description tag, canonical tag, outbound links etc.)
Site factors (Sitemap, Domain trust, server location, site optimized for mobile, integration of Google webmaster tools.)
Off Page factors (no: of linking domains, link relevancy, no: of dofollow vs. nofollow links, link anchor etc.)
Domain factors (domain age, domain history, country TLD)