Where abouts in China are you?
China is so vast/large and with so many layers of people, culture, and history going back 10,000 years, you could spend the rest of your life 8 hours a day "seeing China" and not see but a small percentage of what there is to see. Is like asking, " I am in USA . Any follow-up comments or suggestions on what to do in USA?" You need to be a little more secific.
Example: If in Beijing you must visit the Forbidden City which the Chinese call Gugong which literally means "former palace". To just walk past, not stop and study or go inside every structure within the Gugong would take 1 month full time, 8 hours/day/7 days a week.
There are a lot buildings and sights to see in the Forbidden City as was explained to me when I asked the question " How long to walk by/see every building in the Gugong" of the nice young woman assigned to show me around the Gugong. She was Beijing University graduate student studying for her Masters degree in just "Gugong".
She escorted me to a few of the places in the Gugong that I wanted to see and was brilliant knew every detail about the area I wanted to see which she short cut escorted me to. Was a great day --just 1 day at Gugong to see a little bit of it and get some great photographs.
So what are you interested in, how much spare time do you have to sight see? What City in China are you staying in + are your free to travel to other Cities by train or air plane?