Bangkok is the usual gateway for most travelers, and you should plan on three or five days in the capital. This should allow sufficient time for seeing the major sights such as the Grand Palace and Temple of the Emerald Buddha, Wat Arun, Wat Pho and Vimanmek Mansion. Perhaps also a trip along the Chao Phraya River or a shopping jaunt to Chatuchak Weekend Market. 
The variations for a visit to Thailand are never endless, and perhaps the best advice to bear in mind when arranging your trip is to plan on coming back.

Chiang Mai is a city built on the roots of a traditional heritage that dig deep into the soil of time. It's a city with a beautiful cultural personality of its own. In addition, it's been blessed with much majestic beauty in nature. The people themselves are an unforgettable part of Chiang Mai. Handicrafts of silk, silver and wood are timeless souvenirs for visitors from all over the globe. Along with all this, a wide variety of accommodations, restaurants, and entertainment all help to make Chiang Mai one of Thailand's prime tourist attractions

Krabi is a southern province on Thailand's Andaman seaboard with perhaps the country's oldest history of continued settlement. After dating stone tools, ancient coloured pictures, beads, pottery and skeletal remains found in the province's many cliffs and caves, it is thought that Krabi has been home to homo sapiens since the period 25,000 - 35,000 B.C. In recorded times it was called the 'Ban Thai Samor', and was one of twelve towns that used, before people were widely literate, the monkey for their standard. 

Pattaya is 147 kilometers southeast of Bangkok, and
faces the Gulf of Thailand. Pattaya is Asia's premier beach resort, and caters with equal appeal to Pattaya's relaxing tropical ambience is synonymous with every ingredient for memorable holidays.
Theme and amusement parks, offbeat museums and lush botanical gardens offer numerous forms of leisure activities and cultural entertainment for all family members.
And after dark, Pattaya offers all the allure and magic of a truly vibrant nightlife with a spectacular variety of restaurants, night clubs, bars, discotheques, cocktail lounges and carbarets.
Pattaya can be brash, bold, beautiful and bucolic, and offers everything an authentic international beach resort can.

Phuket, a large island in the Indian Ocean, is 867 kms. from Bangkok. It is the only island having provincial status, and was a regional headquarters as well, with a rich and colorful history.
Known as the Pearl of the Andaman, it derived much of its former glory and its enormous wealth from tin production, which in Phuket dates back over 500 year. Today, Phuket is the major tourist attraction of Thailand. The surrounding waters contain much varied  marine life, and the town is notable for its Sino-Portuguese architecture. It is a very attractive island for sightseeing, with lovely seashores and forested hillsides. Its population of 1.6 million people ranks sixth among all provinces. Approximately 1.75 million Rai of the area is forest land. The main occupation here is rice farming. The average per capita income is 14,343 baht.

Learn more about Thailand at www.tat.or.th