The best piece of advice I can give you before you go : learn a few basics in Mandarin. It will help you to make the most of your trip. Outside the big cities it is really difficult to communicate with the Chinese, and they are always grateful for your efforts, even if they don't understand a word you say! Don't forget to take a small dictionary with you to reinforce what you say.
To have a successful trip, my best advice is to avoid faux pas and be aware of a few practical things. Here are 4 things that I think are important:
Don't tip in a restaurant or taxi. Don't even try it, as some Chinese will be offended.
My final piece of advice to travelers : the Chinese are very modest and it's rare that you will meet anyone even holding hands in the street. So, avoid public demonstrations of affection, as they will make everyone feel embarrassed.