Traveling in Beijing is a nice choice and you can enjoy yourself in the scenic beauties and historical interest. However, there are still something should be paid attention.
Beijing is a very safe city. However, tourists are often preyed upon by cheats and touts. Be especially cautious in the inner city, around Tiananmen Square, and on the tourist-crowded routes to the Great Wall.
For tours to the Great Wall, be wary: the driver might just stop and set you off before your destination. Only pay afterwards if you are absolutely sure you are at the destination. Do not go for organized tours to the Great Wall in the 100-150 Yuan range that is advertised by people handing out flyers around the Forbidden City.
Be wary of fake money. You may observe Chinese people inspecting their money carefully, and with a reason: there are a lot of counterfeit bills in circulation. The most common are 100's and 50's. A few tips for identifying counterfeit bills:
Be very careful if someone wants to give back the largest currency bill (50 and 100 Yuan) by the excuse of "no change". In an attempt to pass you a counterfeit bill they may tell you that they have lowered the price in your benefit.
Take care about meeting "students" who direct you to tea sampling shops. It is free to sample tea for locals, but for tourists...you should ask.
Legally, pedestrians have the right of way on zebra crossing, although just a few drivers will actually go the mile and stop for them. It is better to cross via an underpass or an overpass. To appear on the traffic light (for pedestrians), and cross when the lights turn green.
Drinking lots of the local green tea (hot) will help you resist sickness from the bad air. Green tea has antioxidants, some vitamin C, and the hot water helps to moisturize your throat. Winter is the worst time; cold air creates an inversion layer and traps the pollution in the city.
Bring a pack of your own tissues (or toilet paper) and small bar soap. Many public bathrooms do not have toilet paper, especially if you venture out to the countryside. Alternately, you may wish to purchase an alcohol-based hand sanitizer for quick clean-ups. Also, pre-packaged wet hand wipes are indispensable.
Try to use the bathroom before you leave for your destinations. Some establishments will not have Western style toilets, and many a lady has been shocked and dismayed to find she doesn't know how to use non-elevated (sunken) toilets.
In dryer months (especially winter), be sure to bring or purchase a heavy moisturizer. Although most hotels will offer some generic brand, the quality varies greatly and you would do well to supply your own. It is advisable to purchase and drink several bottles of purified water a day.