The preceding answers are all very good. I agree particularly about the advantages of having such a long coastline. Russia, for many years, felt handicapped because it did not have easy access to the sea at its western borders. The Pacific coastline of Russia is far from its major cities. The Chinese are fortunate to have such great access to the Pacific Ocean. Countries without easy access to the sea are at great disadvantages.
One would think that an advantage of location would be breadth of location, size, but it hasn't always been the case. One would think a disadvantage of location would be the proximity of Japan and the Southeast Asian countries, but it hasn't always been. One advantage that seems unvarying is China's Pacific Ocean shoreline, which covers vast extent. One disadvantage that seems unvarying is the natural boundaries, such as mountain ranges etc, within the country, which cut Chinese groups off from other groups.
I'll answer from a geographic point of view!
China has three significant rivers, which provide transportation of people and goods to large areas of the country. They also cause huge loss of life and property when they flood.
China is bordered on the east by the Pacific Ocean and on the southwest by the Himalaya Mountains. These features protected China from foreign influences in years past, allowing the Chinese culture to develop as a strong and unified entity. This isolation may be considered both a positive and a negative.
China's huge territory includes a wide variety of climatic zones and topographic formations. China is rich in natural resources and has many potential business opportunities as a result of its resources. Development of industry to exploit those resources has led to serious pollution and environmental impacts.
Certainly historically China's location has meant that it has been subject to various invasions from a number of different nations, and #2 is right in highlighting the way that the Mongols used to attack it on a regular basis. However, at the same time, China's location and its vast territories have given it a number of advantages in terms of natural resources and the ability to seclude itself--which is also a negative.
In modern times, China has been and is surrounded by enemies, or at least countries with which tension exists. India on the southwest, Russia on the north, and Japan off the northeast coast are all countries that China has issues with, so one disadvantage is being in the heart of their enemies.
One advantage is that China sits in the middle of all the major Asian trade routes, and the natural economy that follows those routes has helped to make China into the second largest economy in the world.
There can be many ways to answer this question.
Historically, one of the major negatives about China's location (for the Han Chinese, at least) was its proximity to Mongolia. Because China was so close to Mongolia, it was subjugated by the Mongols for long periods of its history.
In modern times, China's location in East Asia is a positive for it. A major reason for this is that China has a long coast that it can use for trade. China has become strong by trading, particularly with the United States. China's location, with its long coast, makes this convenient. China also (at least nowadays) lacks any major regional rivals for political and military dominance. This is a positive about its location.