There are three main terminals for buses leaving Bangkok, in my situation Mo Chit BTS Station 2 is the main terminal going to Northern destinations.


•From the airport
Just save headache and jump into a cab (meter) located in front of airport exit. You will see people waiting in line and a couple of booths with attendants and cabs lined up behind them. Show the attendant your written or even better 'printed out' destination (easiest way is have it in Thai not English) However, Mo Chit 2 BTS should be easy enough for them to undersatand as long as you pronounce it well.

•From your hotel;
 If you have luggage, take a cab to Mo Chit 2 bus terminal. Cab cost is low and worth the pay rather than dragging of huffing your gear trying to save 30THB. For me the cost was 90THB ($3US) from Watana Mansion Hotel Bangkok to the Mo Chit 2 bus terminal (about 20 minutes).

 

Once there you will see windows where attendants are selling tickets, just look for one that says Chiang Mai and buy the next bus ticket (I think one leaves every hour). I could not read anything else besides the cost of 526THB. They are not the best at speaking English, so I just showed my bus ticket  asking with a smile along the way through the bus loading area until I got to my bus (which did not have my number in English on it). The bus is nice double decker with reclining seats, AC, Thai movie, snacks and drinks, roomy. I took the 1030am bus from Bangkok and arrived in Chiang Mai around 8pm or so.  The ride is somewhat of a boating affect, so you may want to take motion sick pills if you are sensitive to that.  The scenery is nice and small villages are passed, everything looks clean and pleasantly relaxing for a comfortable journey.