All visitors entering Thailand must possess valid passports valid for at least six months from the date of entry. On entering Thailand, visitors must ensure they receive an entry stamp in their passport, as fines for not having one are expensive.
The best way to get entered to Thailand is to apply for Tourist Visa. Arriving by Airplane you can obtain a 30 day tourist Visa. To do this you will need to show you have an exit ticket before the 30 days have expired. The regulation depends on the nationality.
The border checkpoints falling under this category are:
International Airports
-Suvarnabhumi International Airport in Bangkok.
-Don Mueang International Airport in Bangkok.
Thailand-Laos Border
-Lao-Thai Friendship Bridge III, Nakhon Phanom-Khammouane Province.
The VISA EXEMPTION RULE allows tourists from 55 countries to enter Thailand without a visa. They are granted to stay a maximum of 30 days if they are entering Thailand via an international airport or entering through a land border checkpoint from neighbouring countries.
More information at Thai Embassy.