YouTube's recommendation system connects billions of people around the world to content that uniquely inspires, teaches, and entertains. Factors such as clicks, watch time, survey responses and social aspects like sharing, likes and dislikes all play their part in determining how videos are recommended to the end-user.

For a more detailed look at the inner workings and evolution of the YouTube recommendation system, along with a number of frequently asked questions, you can find the below article from VP of Engineering at YouTube, Cristos Goodrow, of great use.

YouTube’s Recommendation System