You don't have to be good at Chinese to know that 老师 'teacher' and 外教 'foreign teacher' are two different words. You don't have to be inexperienced with China to find this creepy.
Here are my seriously fallible points about how not to act. They run contrary to what many people with China-experience will tell you, and maybe I will change my mind on some of them. But here goes:
1. Don't believe what people say about you
You're probably not a wealthy, well-connected person with loose sexual morals. Although most Chinese people will think that you are.
2. Don't feel you have to tolerate your linguistic identity
Finding opportunities to converse in Chinese can be an uphill struggle. Lots of people see you as a toy to practise English with, others will not be able to get their head around the fact that a foreigner speaks their language, and therefore not understand a word of your perfect Mandarin. Be firm and be thick-skinned.
3. Hello is not a swear word after all
This is easy to forget after being in China for a while. No words are bad, it is the way people use them that is bad. "Hello" is a word that is capable of a lot of friendliness and even tenderness.
4. Teaching oral English is a kind of performance
Language teaching always has a visual element to it anyway. I once got indignant about being required to be different to their Chinese teachers, but Chinese youngsters are generally a lot more passive than what a Western person might be used to. "The best teacher makes you forget that there's a teacher in the room" is a good sentiment, but it simply can't work in a class of more than a dozen students. They're looking to you - perform.
5. You are merely leading horses through water
Your school may try to convince you that you are at fault if some Students are uncooperative, or blaming you for unsatisfying progress. I have been directly involved with formal learning for all but a few months of my life, and in my experience, a person who is not self-motivated will simply not learn. You can't build an ark for everyone.
6. You are not the Messiah - honestly
You are here to do a job, not to make dreams come true. The education system here is corrupt in a way that will take more than a generation to fix.
7. You are a plaything - get used to it
You might be an excellent teacher, but that's not why you're sought after. You might be excellent at Chinese, but that also isn't why you are sought after. You are wanted because of wht you look like and the linguistic identity that it carries. People in authority will often seem corrupt and indifferent to/ignorant of the learning process. They might well be. But that doesn't make them terrible people, they were fucked up in their turn by fools in old-style trench-coats.