In general, China is a relatively safe country, no matter what time of day, even for women. Guns are illegal and violent crimes are rare. Over the years, pickpocketing has become more prevalent and it's best to carry your purse or backpack in front of you when going through crowded areas. Although it's rare, burglaries do happen, but mostly before Chinese New Year in January or February. Just always be cautious and make sure to lock your doors and windows when leaving your apartment.

Fake money has grown increasingly popular and as a foreigner, you're an easy target for receiving worthless bills. Always double check your money before leaving a business or taxi.

Watch out when crossing the street! People drive all over; right side, left side, middle side, it doesn't matter. Crosswalks are typically useless, unless you're in a major city, but even then people tend to cross the street whenever they feel like it. Most will swerve around you, but keep an eye out for larger vehicles and walk diagonally with the traffic flow.

The Chinese still rely heavily on herbal medicine. If you're prone to getting sick, do a quick run to your drugstore to stock up on meds before leaving home. If you have asthma, make sure to pack an extra inhaler, especially for the winter months when the air pollution is strongest. Hospitals are efficient, especially for foreigners, but it's a trip you'd probably rather not take if you can help it.

It is a good idea to make sure that you have all of the recommended vaccines before heading to China, as these can prevent a few very serious illnesses while abroad.
For China, it is a good idea to have;

The Hepatitis Series (A and B)
Tetanus
Meningitis (If you plan on living in dormitories)
Typhoid

Two others that are frequently recommended are the Japanese Encephalitis vaccine and a prescription for anti-Malaria pills. These two are more important if you plan on traveling in the south (Yunnan in particular) especially in more rural regions, especially between the late spring and early fall, but are not as essential as the few listed above. If you are only traveling through these areas for a short time, bug spray and long clothing can go a long way in reducing your risk of illness.