There is only one shuttle bus line at Guilin airport, so you could catch the bus easily. And, when you reach the arrival hall, you could find the bus just out of the exit.

The bus's terminal is the civil aviation and has one stop at Guilin Railway Station en route. You could ask the conductor to give you a note then. At the square in the front of Guilin Railway Station, there are some private cars driving to Guilin. But, the cars always stop to wait for other passengers on the way. So, you could walk to the Guilin Coach Terminal which is just 200 meters away from the railway station. Here, the buses depart to Yangshuo directly from early morning to late afternoon every 15 minutes. The bus fare is 15RMB/person.