A few tips...

When you buy a GSM sim card make sure that a) works throughout China and b) can be reloaded anywhere in China. Otherwise you might find yourself with a China Mobile SIM in Ningbo, or wherever, unable to reload.

In terms of your interactions with the police...my experience is that they generally try to help foreigners unless you are being disrespectful. It would not be a good idea to wear t-shirts with bible versus, or something else that might be considered protected speech in China.

When using ATMs, I'd encourage you to stick to machines with attached banks. Very occasionally the machines have eaten my cards and getting a replacement to China can be a bit of a chore.

Once your body acclimates, do not be afraid to eat the local food. One of the best meals of my life was eaten sitting in the middle of a Shanghai street eating fresh crawfish fried in a wok and drinking cheap beer.

Remember...have fun! And report back with your stories.