The three things that make everything else easier

Data first. Almost everything you will do here, from calling a car to reading a menu to finding a pier, assumes a connection. Sort it before you leave the airport if you can.

Cash second, and specifically small notes. Bangkok's cheap and excellent things, street food, boats, market stalls, are cash transactions, and a wallet full of 1,000 baht notes is nearly useless at a noodle cart. Break notes at a convenience store on day one and keep doing it.

Third, save your accommodation's address in Thai script on your phone and screenshot it. A driver who cannot read your booking confirmation in English can read that instantly, and it removes the single most common friction of a first day.

Learn the transport by using it

Do not try to absorb the network from a map. Take one BTS or MRT ride to somewhere you want to go anyway, and one river boat or taxi. Two journeys teach you the gates, the tickets, the direction signs and the rhythm faster than an hour of reading.

The one structural fact worth carrying: the Skytrain and the metro are separate systems with separate tickets, and the old city around the Grand Palace is not on the Skytrain at all. That is why the river boats matter here in a way they do not in most cities.

One landmark, done properly

If the Grand Palace is on your list, make it the morning thing. It opens daily at 08:30 and closes at 16:30, with tickets sold until 15:30, and admission is 500 baht. The dress code is published and enforced at the entrance: no sleeveless tops or vests, no shorts or short skirts, no torn or overly tight trousers, no sleepwear.

Dress for it before you leave the hotel rather than buying a wrap at the gate. The queue is long enough without a wardrobe correction in it, and the same clothing works for every other temple you visit that week.

Pacing the day

Two rules worth knowing on day one

E-cigarettes and vaping devices are illegal to import or possess in Thailand, with published penalties that include imprisonment and fines based on the value of the goods, plus a separate fine for using one in a public place. This surprises visitors regularly, and it is not a rule to test.

The other is smaller and useful: if a restaurant adds a service charge, it must be clearly displayed alongside prices before you order. If it was not shown anywhere and appears on the bill, you are entitled to question it, and there are consumer hotlines for exactly that.