Seeing the whole of Bangkok in one day is an impossible task. A good idea would be to concentrate on some basic parts of the city. Visitors can get a fairly good idea of all of Bangkok's treasures by concentrating on those monuments and sights located in the neighborhood of Ko Ratanakosin. It would be advisable to follow the guide below.
Start early in the morning and make arguably Bangkok's most famous site, The Grand Palace your first stop. The Palace opens at 8:30 in the morning so be the first to get in. There is much to see here perhaps the most interesting site would be the Chakri Maha Prasad where Thai weaponry, the ashes of cremated royals and the throne room are located. Spend at least 2 hours here after which tourists should proceed to the national museum sparing at least 2- 3 hours for this visit. Interesting collections of Thai jewelry, ceramics, and sculptures are located here. Be sure to visit the Transportation Room.
Grab a quick bite at Rub Aroon located in the vicinity and head over to see the Temple of the Holy Jewel Image where the emerald Buddha sits on a fantastic gold altar. Be sure to fit this trip in before 3:30 P.M which is when this site closes. After that, head over to the Reclining Buddha and be sure to drop coins into the begging bowls for good luck. This site remains open till about 5: P.M.
You are likely to be exhausted at this point but no trip to Bangkok is complete without visiting one of the famed shopping areas. Head across town far from the Ko Ratanakosin neighborhood to just beyond Lumphini Park where Suan Luam Night Plaza consisting of a number of stalls is located. Buy a few Thai souvenirs. After that proceed to Ratchdamri Road located nearby and go to either the Chinese Restaurant or the Spice Market for dinner.