If you flight to Thailand you will probably land in Bangkok Airport (Suvarnabhumi airport), and then you will want to head to Kao San Road, the main backpackers hub.
Airport Rail Link + Taxi
The best option is to use the Airport Rail Link from the Airport to Phaya Thai Station (the last one). The train is pretty fast (30 min) and costs 45 BHT (City Line). You can find more info at their website.
From Phaya Thai, you will need to flag down a Taxi and ask him to take you to Khao San Road, if he wants a fixed price it has to be between 70 – 100 BHT (no more than that) if they don’t accept ask for the METER. Taxi drivers and tuk-tuks love to overcharge tourists as we described previously.
You will notice that when you go out from the station there are going to be some taxi drivers waiting for tourists DON’T TAKE THOSE CABS, just continue walking to the main avenue and flag down a common one.
Look for the Train Schedules since they don’t run during some night hours.
Special shared taxi
You can maybe catch a bus from the airport to Khao San for about 150 BHT, but they are not always there and also it can take you some time to get to the area because of the traffic jams. So just take the train!