The best overall time for visiting most of Thailand climate-wise is between November and February when it is not too wet and not too hot. The south is best visited when the rest of Thailand is miserably hot (March to May), and the north is best from mid-November to early December or when it starts warming up again in February. If you're spending time in Bangkok, be prepared to roast in April and do some wading in October - probably the worst two months, weather-wise, in the capital.
Thailand shares borders with Malaysia, Myanmar (Burma), Laos and Cambodia. The country's east coast borders the Gulf of Thailand and the west coast abuts the Andaman Sea. The country is divided into four main zones: the fertile, central plains of the Chao Phraya River; the poorer region of the 300m (985ft) high northeast plateau; the fertile valley and mountains of Northern Thailand; and the rainforested southern peninsula. The highest peak is the 2596m (8512ft) Doi Inthanon in Chiang Mai province.
Most visitors can stay for 30 days without a visa.
Like most countries, Thailand prohibits the importation of illegal drugs, firearms and ammunition (unless registered in advance with the Police Department), and pornographic media. Electronic goods such as personal stereos, calculators and computers can be a problem if the customs officials have reason to believe you're bringing them in for resale. As long as you don't carry more than one of each, you should be OK.
A reasonable amount of clothing for personal use, toiletries and professional instruments are allowed in duty free, as are one still or one movie/video camera with five rolls of still film or three rolls of movie film or videotape. Up to 200 cigarettes can be brought into the country without paying duty, or other smoking materials to a total of up to 250g. One litre of wine or spirits is allowed in duty-free.