The City Line rail link offers direct service to many of the neighbors of Bangkok. Leaving from with the Suvarnabhumi Airport terminal (-1 floor) it is extremely easy and fast. A ticket to Ratchaprarop station, the second to last stop, costs 40 baht and takes only 25 minutes.
The city line has a total of eight stops. There is an express train that stops at limited stations once an hour.
We had one night at the beginning if our trip in Bangkok with an early flight the next morning. We decided to stay in the Pratunam neighborhood so that we could walk to and from the Ratchaprarop station and avoid the heavy Bangkok traffic to the airport.
The rail line starts operations around 6 AM, but always check with local service stations for more information. There is also a counter on the -1 floor of the airport that offers maps and more information.