It was a late night flight from Manila to Bangkok (via Cebu Pacific) and we arrived at the Suvarnabhumi International Airport (BKK) around midnight (note that Bangkok is 1-hour late from Manila).
Tips at the airport
Airport facilities such as money exchange counters are still open even at midnight so you can exchange a small amount of money for Thai Baht (THB) in this airport to be used for your taxi fare. You can also bring Philippine peso instead of US dollars. I suggest having the rest of your money exchange for THB at the city itself as they have lower exchange rates at the airport.
Getting a Taxi at the airport going to your hotel
If you have not arranged for a taxi pick-up at the airport, proceed to the first floor of the arrival area. Go outside and you will see a “Public Taxi Desk”. You will meet the main dispatcher and tell him your destination. You can also prepare a printout of the hotel address in Thai characters and show this to the dispatcher.
The dispatcher will then hand you a slip of white paper, keep this and do not give this to the taxi driver. Not sure whether metered taxi is possible during daytime but we were told of a fixed rate of THB450 by the dispatcher (inclusive of the mandatory THB50 to be given to the taxi driver per Thai ministerial regulations, which is on top of the metered fare).
Since it’s already past midnight, you can tell the driver “no highway please” to save you from paying toll/expressway fees (about THB75), which are usually at the expense of the passengers. From the airport to our hotel in Khao San Road was only about 30-40 mins since there was no traffic.