So, you will visit Bangkok ? You will receive many offers for taxis and hotels just before leaving the arrival zone!  Ignore them. Say: "no thank you".  Most of these services are too expensive. After leaving the arrival zone without losing money, you may wish to first visit one of the currency exchange services.   That's ok!  Do it.
To go to Bangkok now, you will need a taxi. There are private taxis called taxi and public taxis called taxi-meter. Take a taxi-meter, because it is much more cheap. Some private taxis pay money to the airport, so they have a better location for waiting for passengers.
Money-Hint: Use the exit on the third floor (departure) and ask an incoming metered taxi for take you to your desired destination. These metered taxis generally come from Bangkok to carry passengers to the airport. Here is the best (and cheapest) place to get transportation to Bangkok central.
How to "use" a taxi: First, tell the driver your destination. If the driver likes that, tell him you want transportation "by meter". If he still agrees, you have your first golden deal. We highly recommend to enter the taxi now!  Let him use the "express road" and give him the tollway fee (40 Baht).Finally, you will pay estimated 250 Baht (depending on destination).
If the traffic is very busy in Bangkok (it happens sometimes...), many drivers do not like to go "by meter". (This is illegal by Thai law and you can report them to any police officer.) Ignore them and move on to the next taxi which is willing to go by the meter. In the case you can't find a willing metered taxi you must bargain for the price. You should not accept more than 70% of his first offer.  Do not enter the taxi before fixing the price!   Finally, you will pay 300-500 Baht (depending on traffic and location).

Hotel: You can book a hotel at one of the counters in the airport, but take note of the location and the price, but this is not the best idea!   Try to book a Bangkok hotel before arriving . . . over the Internet.
Enjoy Bangkok, but please do visit Samui . . .

There are 2 airports in Bangkok: The new Suvarnabhumi (read Suvannapum) International Airport, which serves international and domestic flights, and the old Don Muang Airport which is used byNok Air and One-Two-Go Airlines.

For detailed information about the airports and terminals please go to: Suvarnabhumi International Airport or Don Muang Airport