Ranking Metrics
Let's first consider rankings. There are several types of ranking to consider. I track Google desktop, Google mobile and Bing on most of my sites and each of them gives a different answer because each of them have slightly different criteria or algorithms that they use when assessing your website and determining its ranking.
The criteria used of course are generally fairly secret. If a search engine released its exact algorithms to the public a lot of the website builders would be scrambling to 'game the system'. They also shift gradually over time so what might work one year may not work quite so well the next.