Bangkok Suvarnabhumi International Airport is Thailand's main international airport dealing with the high volume of tourists arriving during the peak season. Other main airports include Don Muang and Phuket with a number of other small airports on the islands. The national airline is Thai Airways but other major airlines fly from the UK to Bangkok. The flight time is 12 hours. If you are already travelling in South East Asia you can get the train from Malaysia and there are connecting routes with Singapore, Cambodia and Laos. The opulent Eastern and Oriental Express runs directly from Bangkok to Singapore but not for the budget traveller.
From the airport, the easiest method of transport is to get a taxi to your hotel. Many tour operators will organise transfers for you from the UK. If you're staying in Bangkok there is a new high speed rail link between the airport and city centre which takes only 15 minutes. There are also car rental counters at all international Thai airports if you dare to experiment driving in Bangkok or further afield!
There is a good public bus service in operation throughout the country. They are low cost - only charging a flat rate regardless of the distance travelled. Bangkok has yellow taxis that are easily identified by their signs saying 'taxi-metre'. The most popular method of travel in Thailand though is the 'tuk tuk'. These are three wheeled taxis are scooters with a passenger cubicle on the back. They are cheap but it is recommended that you negotiate fare prices before you travel. Bangkok also offers a river boat, Skytrain and Metro service. The more rural areas will have less formal transport options, however in most places there will be either tuk-tuks or rickshaws.
Thai airways has internal flights operating to 15 airports in Thailand both on the mainland and to the islands. Flying internally may be preferable to long distance coaches and/or trains. They are reasonably priced and flight times to Koh Samui (for example) are less than an hour. Coaches are another popular mode of transport. Fares are cheap and buses are plentiful. There are varying standards of coach but often they are crowded. The coaches are best booked in person from the bus stations. The rail network in Thailand is extensive and well maintained. Trains link all the major towns with the exception of Phuket. State Railways of Thailand manage the rail network through Thailand. Some of the trains have air conditioned, sleeping facilities with a restaurant/food cart to help with the longer journeys. The southern line stops at Surat Thani - the port that acts as the gateway to the islands of the Eastern tip of the country.