The reality of how things really are in mainland China, vs. whatever you have read, seen, or been told about here while in your home country. The two concepts are as different as night and day.

Jettison whatever you expected. Prepare yourself to be shocked, amazed, angered, pleased and annoyed by what you see and experience in day-to-day life around you. Some things will be a pleasant surprise, other things that happen will cause you to shake you head and think, "Was I crazy?"

Always keep in mind that China is changing. Fast. For good or for worse, she and her people are traveling somewhere at breakneck speed. The end result is not clear, but eventually (maybe not), the dust will settle and the nation will be what it will be. Whether socially or existentially, the Chinese will continue to do things their own way, as they see fit. Don't concern yourself too much about what will happen. Carve out your space, treat others like you want to be treated, and enjoy your time here!

Giadrosich has nailed it here.

Don't underestimate how different things will be from home. Be prepared to go easy on yourself for the first few months; don't expect to land and immediately feel at home and settled.

Also, be aware that you will not be exempted from being lied to and having your contract 'adjusted',  unless you're seriously lucky. It's not just a stereotype, it's how things work here. Be prepared to look out for yourself and to defend your interests.

If you are planning to live a hermit life even then you will still have surprises awaiting for you. You walk out on the street walking to your school you see a kid taking a dump on the pathway is an example and many to add just by going back and forth to school and your home.

If I had a one rmb for every time I've heard a foreigner coming to China say the same thing and change their entire lifestyle in one year, I would be able to buy that ticket on the big gray boat for the upcoming 2012 doomsday date. You will never know until you get here.

That is basically me, without the knowing Chinese people back home. Even though I had read many blogs on every day life in China, there was still a heck of a lot of culture shock. Even if you know what to expect, it's a whole different experience living it. It will not be hard to avoid smoking, drinking, and the like, you just have to be insistent. Don't think that you will be insulting their culture by refusing a cigarette or a beer, you just have to be polite and know a good way to refuse it without them losing face. If you are a girl, that won't be an issue, as I'm never given a cigarette and rarely offered beer. Breaking laws is pretty common though. You're going to jaywalk, it's kind of what everyone does. The locals don't follow a lot of the small laws, and they'll never get in trouble for it. What you have to remember is that many laws are flexible. There are also unwritten social laws that people follow that you may not be aware of.

Expect to make mistakes, socially and while attempting to speak the language. Expect to get the runs for about a month after you get here. Expect that when you make a real friend, they will do whatever they can for you, but there will also be many people who just want to be "friends." Expect to get homesick, even if that's never happened to you before. Expect to get lonely sometimes, even if you keep in contact with people from home. Expect to be surprised and shocked often at first; those moments will eventually just be TIC (This is China). Expect to have days where you will hate China, but also days where you love it. Maybe you will get sick more often (I sure do). Don't be surprised when the reasoning for all the food/health related things they do are based off of Traditional Chinese medicine, because they will sound silly or illogical. Don't be surprised if people tell you what they expect you to be like; maybe they will say you are not shy or that you are outgoing, even if you aren't. Don't expect the Chinese to have any skill at measuring time or how long something will take, because they are often wrong, especially when it comes to what they will do in a city while traveling; many do not plan ahead.

And I guess, most important of all, expect your views on the world, especially of China, to change, because you had no idea that there was a part of the world where people think and live completely different from what you are used to. Expect the unexpected is not strong enough advice. It's more like expect to go on an adventure comparable to a tall tale, because some of the things you may experience will be unbelievable to anyone who has never lived here themselves.

No what I meant was, I've heard many people say what they would and wouldn't do here, and it generally changes after a year.

Just to add to the above-mentioned points, you probably should consider taking up drinking, smoking and promiscuity if you are a guy. Not doing any of those are three qualities that scream "I don't want face". and you will be a 98 hour/week slave for less pay than your contract states.

Kchur so correct. I started smoking a year ago, never smoked before, drink white wine during every meeting because I have to, but on the bright side, I dont have to work the 9 to 5 a typical person would, I have two hour lunches and I go home at 3:30, one hour after my lunch is over. Although there has been some long nights pleasing the customers at the KTV or club but hey, we do what we have to