If you are flying from other Thai cities to Bangkok, chances are you will land in the smaller airport, Don Mueang international Airport. From there, if you are heading to the city centre or Khaosan Road, you have three options.
Luxury: taxi service: 300-400 bath; tale the official taxi service from the taxi counter.
Medium: limo service: 150bath per person, from the information desk.
Dirt cheap: A1 bus to Mo Chit BTS terminal and then one of the bellow buses to Sanam Luang Park or Khao San station: 30bath +15bath pp.
the A1 station is just outside of the Arrival gate, the station is appropriately marked.When you get off the A1(less than 10min ride on the highway) at the Mo Chit BTS station, walk in the same direction a little bit till you reach the bus station(past the stairs going up for the train).
Buses that go from Mo Chit to centre:
3, 44, 59, 503, 509, 157, 524.
The white paper below was at Mo Chit bus station probably put there by a kind traveler to help others. The buses listed coincide with the official paper, listing which buses reach the park or Khaosan plus the fare for each.