From airport terminal, you have to take Airport Shuttle Bus (Bus No.: Ordinary 1, Ordinary 2, Express 1 & Express 2) to the Public Transportation Center. FREE service.
From Public Transportation Center, you will be able to choose from the following buses that bring to downtown Bangkok:
1. Route 549 Suvarnabhumi-Minburi
2. Route 550 Suvarnabhumi-Happy Land
3. Route 551 Suvarnbhumi-Siam Paragon
4. Route 552 Suvarnabhumi-Klong Toei
5. Route 553 Suvarnabhumi-Samut Prakarn
6. Route 554 Suvarnabhumi - Bangkok International Airport/Don Muang
7. Route 555 Suvarnabhumi - Rangsit
8. Route 556 Suvarnbhumi - Southern Bus Terminal
9. Route 557 Suvarnabhumi - Wongwien Yai
10. Route 558 Suvarnabhumi - Central Rama 2
11. Route 559 Suvarnabhumi - Future Park Rangsit
I took the bus Route 551 to Victory Monument and then took a taxi to my hotel. Or you can go all the way to Siam Paragon and take the Skytrain to where ever you want to go.
For more details on the routes, please visit the official website of AOT:
http://www2.airportthai.co.th/airportnew/sun/transportation1.asp?lang=en⊂=bmta#bmta
