By bus

Modern and comfortable air-conditioned buses provide reliable service to every province and all the major towns. Regular and local buses, while usually slower and less comfortable, are extremely reasonably priced. You can buy ticket at every bus terminal (Please note: in Bangkok there are different bus terminals!) or contact any local travel agent to help with purchasing a ticket. Besides that there are mini-buses leaving from Khao San Road to nearly any spot of tourist interest. There are very cheap, direct, but very often very uncomfortable. Besides that you will not meet any local people. Last but not least - coach tours are available with most travel agents.