How did the events of the Tang, Song, and Yuan dynasties influence the chinese social structure and the daily lives and activities of the common people, who were the vast majority of the population?
The Yuans, through their contact with the West, introduced a number of new agricultural techniques and crops that changed the lives of peasants. They also instituted a stronger bureaucracy, which was set up as a sort of military model- just what you'd expect from a militaristic society. While peasants' lives probably otherwise changed little under the Yuans, or any other dynasty for that matter, the connections with the West (it was under the Yuans, after all, that Marco Polo paid his visit) marked the beginning of China's participation in the world maritime trade systems that changed the Old World forever.
The Tang dynasty seems to be a very creative one, with art and poetry. Such things have an influence on the culture of a society, and influence the cultures that follow as well. It may not seem important, but it really is! The influences can be subtle.