There are common travel routes in China which take in the major sights. If and how you follow it depends on your time, interests and budget.
Beijing→Xi An → Shanghai
Following this route you will first see the capital of Beijing with its historic sights such as the Great Wall and the Forbidden City. We recommend 3 to 5 full days. Then you fly or take the overnight train to Xi'an and see the Terracotta Warriors, the old city wall and other sights if you wish. One or two nights at most in Xi'an. Then fly or train to Shanghai where you see China's most modern city. Two nights in Shanghai is a good amount of time. With this itinerary you can internationally fly into Beijing and out of Shanghai. The route can also be reserved.
Other routes generally add onto this plan. We can custom tailor an itinerary for you. Popular add ones include：
Guilin &Yangshuo (1 to 3 nights) - Guilin is a big city which is crowded with Chinese tourists. We recommend either spending 1 night or entirely bypassing Guilin and going straight from the airport the the country town of Yangshuo. Great for seeing the countryside, Yangshuo offers a break from big cities. You can do bamboo river rafting, hiking, caving and biking. An excellent family destination.
HongKong(1 to 3 nights) - You can fly in or out of Hong Kong as one end of your journey. Hong Kong is about triple the cost of traveling in mainland China so if you are on a budget then be wary. Hong Kong is actually very easy to tour on your own as English is widely spoken, so if you are well traveled you may be satisfied to discover Hong Kong on your own and then just fly into China to begin your tour.
Yangzhe river cruise(3 or 4 nights) - See the scenery of the mountains and the three gorges dam. While popular if you have seen magnificent scenery in your life you may not be so moved by it.
Tibet (3 - 14 nights) - certainly a unique and colorful destination, it is sometimes closed without warning by the Chinese government due to unrest. However its quite safe for tourists and a great family destination.