Thailand has been welcoming travellers for so long that it has perfected the art. It is easy, affordable, and astonishingly varied, and it manages to please first-time visitors and seasoned travellers at the same time. The trick is knowing that there are several very different Thailands to choose from.
Few countries do range this well. There is the electric energy of Bangkok, the calm temple-dotted hills of the north, and islands that swing from full-moon parties to silent hidden coves. And running through all of it is some of the best street food on the planet.
Bangkok for markets, temples, and food. Chiang Mai and the north for mountains, monasteries, and a slower pace. The Andaman coast (Krabi, Phuket, the Phi Phi islands) for limestone cliffs and clear water. The Gulf islands (Koh Samui, Koh Tao, Koh Pha Ngan) for diving and beaches. Pick a city and an island and you have a perfect trip.
November to March is the cool, dry, and most popular season. The islands on the two coasts have slightly different weather patterns, so a little planning helps if beaches are your priority.
Eat where the queue is local and the menu is short. The best meal of your Thailand trip will probably cost less than a coffee back home, served from a cart on a side street.