If you are in Nan town you can take the red bus at the Nan bus station. From Nan to Pua it takes about 1 to 2 hours travel time, 70km. These red buses travel every hour during daylight starting from 6 am to 6 pm. If you land in Nan Airport, you can walk (1km) from the airport to the main road and wait for the red bus at the opposite side of the road (towards the North), this means you do not have to go into Nan town (southern direction). For some flight which might land in Nan airport quite late, you have to be fast to catch the last red bus (6 pm), otherwise, you might have to stay overnight in Nan town, and take the red bus on the next day. Please tell your transport driver to drop you off at Seven-Eleven shop in Pua.
*When you exit the Nan Airport building, that is not the main road yet. Please walk towards the right of the building, and it takes about 5-10 minutes by walking distance to arrive at the main road, do not hesitate to ask if you are unsure about which direction to take.