After years of people asking "WHAT DO YOU WANT FROM ME???" Google Search Quality Senior Strategist, Andrey Lipattsev, finally revealed the Top 3 ranking factors. They are:
Links and Content were easily predictable considering the existence of Penguin and Panda respectively. If your clients had any doubt about the importance of links and content in 2016, you can now show them Google this video.
RankBrain is the artificial intelligence part of Google's algorithm that launched late last year.