Trip from Guilin Airport to Yangshuo:
There is a shuttle bus that goes straight from Guilin airport to Yangshuo (1h30min, 60CNY). Departs at 09:30 - 11:30 - 13:30 - 15:30 - 17:00 - 18:30 - 20:00 - 22:30 daily. It stops at Yangshuo North bus station. From there it is about 500m to the city center, so you can walk, or take one of the yellow open mini buses that will take you anywhere downtown for 1Y.
If you arrive too late or prefer more comfort, then it is best to negotiate a taxi (1h, 250-300CNY). Our recommendation is to arrange it previously with your hotel in Yangshuo. They usually charge a fixed rate of 300CNY. But you will avoid having to negotiate with the taxi drivers at the airport: they will try to charge you more money, they tend to have worse cars and they know nothing in Yangshuo, so they will leave you at the bus station, where you'll have to arrange another transport to your hotel. You may be asked if you want to use the highway or not. It is additional 30CNY, but will save you half an hour in the road not to mention countless bumps, so it is definately worth it.