When first traveling to a new country culture shock is inevitable, especially in a place like China, so drastically different from the western world. Reading and researching will never be the same as first hand experience, but knowing what to expect with these tips will help prepare you and soften the blows to your senses.
The average mattress in China seems to range from firm to rock hard, and is much thinner than a typical western mattress. This can be quite surprising when you dive into you new apartment or hotel bed to relax after completing your long and exhausting journey, only to be greeted by a hard thud. I personally prefer a firmer mattress and got used to it quickly and sleep great. But if you prefer a softer bed don't worry, down feather toppers, memory foam toppers, and various other cushions and pads are widely available. You can even buy western mattresses in larger cities pretty easily now a days if you are staying long term and miss your old soft mattress.
It's common knowledge chopsticks are the most used utensils in China so it's nice to make sure you can use them at least a little before arriving. Unless you are eating at a particularly fancy or western restaurant there's a good chance chopsticks will be the only utensil available (with the exception of spoons for soups). So unless you plan to bring a fork with you everywhere learn to use chopsticks as best as you can, and learn what chopstick faux pas to avoid. I thought I was a chopstick expert before trying to eat some particularly slipper dumplings and vegetables a few times and getting laughed at by my Chinese friends. So learn a little and eating out will be much easier.
Plastic stools are everywhere in China and many other parts of Asia. They can range from full size plastic chairs, to backless bar stools, to tiny stumps you can barely sit on. Usually brightly colored and sometimes featuring pictures of cartoon characters or decorative patterns. Expect to find this type of seating at most street food places and many small restaurants. Many other places have stacks of these reserved as back up extra seating too. People hang out all over town playing cards, mahjong, and gambling on these little stools too. If you are tall like me, they can be hilarious and awkward to get comfortable on at times, but just think of them as part of China's charm.
Something you will definitely notice and probably never get completely used to is spitting. People will spit anywhere and everywhere in China. It isn't considered rude or disgusting here, rather it is seen as a normal bodily function and associated with health. People spit to clean out their throat and nasal passages of pollution and other contaminates, the usual precursor is loud throat clearing. Expect to see and hear this walking around town, in elevators, at restaurants, and so on.
China now has a population of 1.35 billion making it the words most populous country. Most of this population resides in cities in the eastern half of the country making the concept of personal space very different and much more limited. When waiting in a line in China, a line can be standing only a few centimeters behind the person in front of you or it can be a big amorphous blob steadily working its way forward. If you are waiting in line anywhere in China keep this in mind and stand close to the person in front of you or people might not realize you are waiting and cut right in front of you. Also with personal space, girls will often walk around arm in arm or holding hands and guy friends might have their arms around each other. Personal space here is relative and more casual, so don't be worried if you occasional touch or bump into others in crowded places.
China is by far the loudest country I have ever been to. With the exception of the rural countryside, life in China is pretty noisy. Traffic is crazy which leads to constant and sometimes excessive honking. Late nights quiet down a bit but rush hour and busy areas near main streets are especially loud and crazy. The way many people talk and express themselves can be considerably louder than you my be used to, depending on where you are many conversations often sound quite loud and excited. China also invented gunpowder and fireworks. During festivals like Chinese New Year firework sales go way up and they can be heard going off nonstop, so don't except a quiet nights sleep amongst all the celebration. But it's really fun, and you'll get used to it like everything else.