By plane
Most visitors to Thailand will arrive at Suvarnabhumi Airport, Thailand's largest airport 15 km 19 miles east of Bangkok. It is roughly a 45 minutes ride from the centre of Bangkok, but heavy congestion could make that trip into 1,5 hours or more. More information about the airport can be found in the Bangkok article.
The easiest way to get into Bangkok is by Airport Express Bus: the ticketing booth at the first floor sells flat 150-baht fixed-fare tickets to Bangkok's four main districts. You can also wait in line at the queue for a metered taxi at the first floor, a trip to the city costs about 250-400 baht. Always use the official taxi stand though, and make sure the meter is turned on, else you might get in trouble later on. In the future, a train line will open from Suvarnabhumi Airport that directly connects the airport with Makkasan station in downtown.
By car
The Central Plains has good road connections with the east, south, north and northeast of the country.
Two main roads connect the Central Plains with Eastern Thailand. The main road is Sukhumvit Road, also known as Route 3, which starts in Bangkok and via Pattaya reaches all the way to Trat and the Cambodian border. Another route goes east to Aranyaprathet from which the border with Cambodia can be crossed to Siem Reap and Angkor Archaeological Park but don't even think about driving on the Cambodian part.
From Phuket, Krabi Province and other destinations in Southern Thailand, take Route 4 that enters the Central Plains right after Chumphon. Passing Hua Hin, Cha-am and Samut Songkhram, the long ride reaches Bangkok.