Here is useful information for individual travellers on how to get the public transportation to Bangkok City and the City BUS Terminals from Suvarnabhumi Airport. Follow the links below;

Wat Phra Kaeo 
https://www.youtube.com/watch?v=MU_DYCp8gys  

Khao San Road 
https://www.youtube.com/watch?v=BoiwbaD30tQ 

Bangkok Bus Terminal (Ekamai) : The Eastern Bus Terminal 
https://www.youtube.com/watch?v=edJYB4PFFKU 

Bangkok Bus Terminal (Mo Chit) : The Central, Northeastern, and Northern Bus Terminal 
https://www.youtube.com/watch?v=Nsh4itFSZj4 

Bangkok Bus Terminal (Sai Tai Mai) : The southern Bus Terminal 
https://www.youtube.com/watch?v=XQ_HTXPukBU