You will find buses in many different shapes and conditions. From the ultra-modern VIP buses with TV and entertainment consoles in the seats, as if you were on a long distance flight, to old bangers resembling something that were discarded in the west 30 years ago.
The ultra-modern buses typically run on long routes, while you typically will find the most dilapidated buses in local routes.
Long Distance by Bus
Although you can get plenty of comfort for almost no money, I would only recommend long-distance bus travel if there isn't a domestic flight to your destination and if your credit card is being strained, and you either do not have time to take the train or if there isn’t a train to your destination.
The journey by bus can be very dull; also, the drivers drive fast and hazardous.
You cannot complain about the price, though. For example, you can travel 600-800 kilometres (375 - 500 miles) in a 24-seat VIP bus with toilet and air conditioning for 1,000 baht (€26/$28/¥190/руб 1.823), which may for example be from Bangkok to Phuket or from Bangkok to Chiang Mai. Such a trip typically takes 10-12 hours. If you choose a bus with more seats (less room for you) and no toilet, the price is about the half.
Do not buy your ticket from a tour agent. You will probably pay too much, and you cannot be sure that the quality of the bus is as promised. Instead, buy the ticket directly from the bus company. Be sure to bring a blanket if you are travelling in a bus with air condition - typically, the driver will set the air condition to "freeze".
There are several bus stations for long-distance buses in Bangkok, thus it will be a good idea to check which one serves buses for your destination beforehand. You can find an overview of routes, prices, and travel length at 1stop Bangkok.
In Phuket, the bus from the beaches at the west side of the island and to Phuket Town at the east side cost around 30 baht. The buses are old, probably resembling a bus from the 60's in your own country. Besides, because of their condition, they probably would be illegal in your country. However, they do run here, and accidents are rare on those routes.
The bus in this picture is one of the newer ones on the route between Patong and Phuket Town. It is actually not a bus; it's a truck with benches and a roof.
In many cities, you will not even find buses like this; instead, they are using songthaews as buses. A songthaew is a pickup truck with benches and a roof. Even in Chiang Mai, the second biggest city in Thailand, they use songthaews instead of real buses.
Buses in Bangkok
In Bangkok, they do have buses, even real ones instead of the trucks with benches. In addition, it is extremely cheap to go by bus in Bangkok. However, the trip may take some time due to the incessant traffic jams, and your lungs will have to recycle the exhaust gasses from the other vehicles, as the windows are usually open in the buses.
If you want to avoid traffic jams, you can use the metro / sky train, or you can take a motorcycle taxi - the latter provided you have nerves of steel and you have paid the rates of your life insurance!
It can be a bit of a jungle to know the prices for buses in Bangkok, some buses / routes operate at a fixed price, regardless of how far you go, others have varying prices. The prices range from 7 baht to just over 20 baht for the ordinary buses.
You buy your ticket in the bus from a ticket seller. Make sure you have small change as you in most cases will have to pay the exact amount, otherwise, they will ask you to get off the bus. I have experienced that the ticket seller would not even agree to keep the change, I had to get off at the next stop.
You will also find minibuses with closed windows and air conditioning on scheduled routes; they charge a slightly higher price. When a minibus stops, the ticket seller will come out, yelling the destination in order to attract customers.
Please note that the regular buses do not automatically stop at the bus stops, even if many people are waiting there. In order to make the bus stop, you hail it the same way that you hail a taxi in Thailand; by holding your arm out downwards, and waving your hand.
Use Google Maps
It can be difficult to navigate the various bus routes for tourists, as they use Thai characters on the buses and at the signs at the bus stop. Google Maps can help you find the right bus routes, and if you use Google Maps while driving, you can plot in your destination and see where to get off.