You will want internet on your cell phone – for maps, for bus routes, for tips on restaurants and shopping, and especially if there’s more than one person in your party and sometimes’s you’ll be split up.
If you brought an unlocked cell phone that’s GSM compatible, you can get set up right at the airport. If you plan to spend the bulk of your time in Bangkok, the best carrier is TRUE/MOVE, which is 4G. If you plan to go to the beaches in the south, you may want AIS or DTAC, which in many areas are 3G.
Assuming you arrive at Suvarnabhumi airport, you’ll find all three major cell-phone carriers right outside the immigration exit on the main concourse (which is on the second floor of the terminal) to get a Thai SIM card. After you pick which plan (make sure to get internet), hand your phone to the staff and they will change out the cards, key in all the codes needed to implement the carrier, and hand you back the phone all ready to go. Just remember to write down the Thai phone numbers for everyone in your party. It will cost about $10-15 US dollars for a week for each phone, and about 1,000 baht (a little less than $30) for a month.
Before you leave the second floor, go to an ATM and get some cash. The debit card you brought from home will work, with the same PIN you use at home. Get a minimum of 3,000 baht. But since all you’ll get are 1,000 baht bills, and since some cab drivers may claim to not have change for a 1,000, you’ll want some smaller bills. So go upstairs to the third floor in the terminal and buy a sandwich or something so they give you some smaller denomination currency. Then go down to the first floor of the airport to the taxi stand. They’ve got a machine that gives you a number for your taxi. The number is the number of the stall where the taxi will be parked. The numbers are suspended from the ceiling of the parking garage, right in front of the machine that give out the numbers.
When you get to the taxi, tell the driver where you’re going. Or, better yet, show the driver the map you printed out at home that has the location where you’re staying.
Expect the cab ride to cost about 300 baht if you’re anywhere near the city center – the equivalent of about $9 USD – plus highway tolls – about another 75 baht. The driver will ask you to give him the money to pay the tolls – all the more reason to have smaller denomination currency. If you’re leaving the airport for town late at night (after 11:00pm), tell your driver “No highway”. It will take only a few minutes longer to take the surface roads rather than the expressway, and it will save you a few dollars. But if you’re coming into town in the day, pay the tolls – it could save you 30 minutes to an hour.
It will take 30 minutes at night or an hour or more in the day to get to into the central city.