China becomes increasingly important in our world. It's advisable to follow China's GDP growth because everything depends on it. If China does well, the whole Asian continent will do well, commodities like iron ore, gold, silver, copper will go up. The Australian economy and its currency depend on China. Emerging markets like Vietnam, Taiwan, Thailand, etc... will do good.
To predict Chinese GDP growth, we can look at the monthly Chinese power output/consumption numbers because there is a clear correlation here.