You don't want to ruin your trip to China and you certainly want to avoid a bad stay. Consider the Yin and Yang of it all; no trip to China is without its highs and lows. To maintain the highs and keep the lows at a minimum, here is a little advice to help you enjoy your trip to China.
1. Getting grossed out
2. Forgetting to put your definition of "rude" in your back pocket for the tripIt is rude in the West to spit, belch, shout and shove. Not so in China. Don't be surprised if you hear a loud hawk as a bicyclist rides by preparing to expectorate or a healthy satisfied burp from your taxi driver as he nods acknowledgement of your destination. These attributes go part and parcel with the merry and demonstrative Chinese people. You don't have to embrace these quirks, but accept that cultures are different. And difference is good.
China is made up of 23 provinces with many dialects and a huge amount of internal migration. While Mandarin Chinese is the common language, many people at home speak a dialect. Therefore, Chinese people are used to being flexible with their language and welcoming to those who try to speak it. A few words go a long way. Even the shopkeeper from whom you are trying to extract a lovely vase at a tenth of the price she asked for it, will smile when you say "tai gui le" (too expensive) in Chinese.
4. Skipping the street food
Of course you should take precaution when eating anything you're unused to. But skipping out on street food snacks in China is like missing out on the Great Wall. Food is important to Chinese people, a colloquial greeting goes "have you eaten yet?" Most of the time, street stalls make the food fresh and sell out quickly. Don't buy it if it looks like it's been standing out for a while or the stall looks particularly filthy. And look for folks standing in line, this is a good sign. Read more about Water & Food Safety in China.
Pack light! You don't need much for China and you will certainly come back loaded with treasure - the shopping is fabulous. China is a casual place. You won't need to dress up too much when dining out and you want to be comfortable for the site-seeing and walking you'll be doing. Bring the essentials: comfortable shoes, sun protection, comfortable clothing, your medical kit and toiletries. But leave room for the hoard you will very likely pick up during your stay: chopsticks, silk, porcelain, jade, pearls, embroidery...