FOREIGN DEVILS WILL BE PUNISHED UPON ENTRY, CHINESE TRAITORS ESPECIALLY SO. Haha, just kidding!
if you don't speak/read/write Mandarin, then you're in for a rough time. (Imagine moving to any foreign country where you don't speak the country's language.) Now, you can stay in one of the expatriate communities (consisting of resident foreigners from other countries), where you can be surrounded by other English speaking foreigners... in which case you do an internet search for expat-communities in China (to get an idea of day-to-day life and expectations.) Being ethnically Chinese (I assume you look Chinese), but being unable to speak, be prepared to receive different treatment. When my ABC friend visited Beijing, most locals he encountered quickly lost patience with him because he can understand but not speak Mandarin. An obviously white/foreign person would not have the same problem, because locals would immediately recognize him as a foreigner.
If you do speak/read/write Mandarin (excellent!), then you['re just like 1 of the other 1.3 billion Chinese people living in China
I think it's important for people to accept that being proficient in 2 languages isn't some kind of magic ticket to better job. Your better opportunities will come from having a superior pedigree (US university diploma), and some demented notion that many western-educated Chinese in China are magically more wealthy and better connected than local Chinese. (Unfortunately, "personal connections" are still really important in Chinese private enterprise.)
Honestly, though, the most important thing to remember, is that every country has its own unique identity. As long as you are courteous and conscientious of social norms & customs, you'll do fine.