Even before you arrive in Bangkok you would be wise to check upon the visa requirements for your particular nationality. Most persons of western nationality however will be provided automatically with a 30 day tourist visa. On expiration of this Visa you will usually be able to extend it at the Immigration centre on ‘Suan Plu’ Road in downtown Bangkok for a maximum of 14 days. After this period expires visitors would than have to leave the country or risk being fined. If you know you are going to stay for longer than this period consider applying for a visa in advance from your home country where double entry and triple entry visas maybe available for you. A double entry visa if extended in Suan Plu twice can get you up to 6 months on a tourst visa whilst only leaving the country once.
If you arriving via the International airport be aware that you will immediately be accosted by the usual army of touts offering you taxi services and so on. A metred taxi should cost around 300 baht to downtown area but you will most likely have to negotiate a fixed price for the journey as the Taxi drivers realise they have a captive market and will be unlikely to settle for the metred price. Many travellers arrive weary and are in no fit state to do the currency conversions in their head so it pays to have a bit of fore knowledge. $10 at the moment gets you roughly 300 baht and 10UK pound will get you in the region of 600 baht. One final tip when handing over 1000 baht notes say the amount out loud so they are aware that you know it is a thousand baht note and they don’t give you change for the wrong amount. It can be suprisingly easily to be short changed when using unfamiliar notes, especially with jet lag!