In Bangkok, for sleeping, there are thousands of hotels and hundreds of guesthouses. Whatever is the area of the city you choose you will have no trouble finding a room in Bangkok even at last minute. It is however better, especially for a first trip to Thailand, to book at least your first hotel in Bangkok night
in advance. The most popular area to stay for travelers is Khao San Road, which is known as the backpacker district. This is where you will find the largest concentration of cheap hotels and guesthouses and also the greatest concentration of tourists of course. Khao San has the advantage of being next to the Temple of the Emerald Buddha
(Wat Phra Kaew) and the Great Palace. I recommend to avoid accommodations located in Khao San Road itself. Personally, I much prefer Soi Rambuttri which is a 2 minutes walk away. The second most popular area for tourists is Sukhumvit district. It is crossed by a subway line and an underground subway line so you can easily get around Bangkok. The prices of the rooms are more expensive and there are logically less backpackers. In general, try to stay near a BTS station, the Bangkok skytrain to be able to get around and reach Bangkok airport easily.