Order matters here. Several items block others, and doing them out of sequence costs you a week.
Before you board (this is still part of day one). Visa approved and printed, passport in hand, insurance policy active from the date you fly, Wise account open and funded, and — if you are on a tourist entry — your onward ticket and funds statement printed and in your carry-on, not buried in cloud storage on a phone at 3% battery. Book the airport transfer in advance with Welcome Pickups if you are landing at night with luggage; it is the one arrival expense that reliably pays for itself in not being scammed at 1am. Install and switch on NordVPN before you leave, not after — you will be on hotel and café Wi-Fi constantly, and some home-country banking and streaming services behave badly from a Thai IP.
Days 1–3: land, sleep, do not sign anything. Book a hotel or short stay for two weeks, not a year-long lease. Use Trip.com, Travala or Aviasales for the flight and first stay. If you are apartment-hunting between check-out and check-in, Bounce and LuggageHero let you dump bags for the day rather than dragging them round viewings. Get a local SIM in the first 48 hours — everything from apartment viewings to bank appointments assumes a local number, and that is the block: no number, no viewings, no bank.
Days 3–10: neighbourhood first, apartment second. Spend a week in the area you think you want before committing. Test the internet at the actual address at the actual hour you work — this matters most on Koh Phangan (~60 Mbps) and least in Bangkok (~230 Mbps) and Chiang Mai (~210 Mbps), but test it everywhere, because the city average is not your building. Visit two or three coworking spaces on day passes before buying a month at $90–$130. Only then sign a lease, and ask for the deposit terms in writing.
Days 7–20: the paperwork that needs an address. Most of the next steps — bank account, longer-term rental agreement, any immigration extension — assume you have a confirmed address and a local number. That is why the lease comes before the bank and not after. If you are on the ED visa, the in-country extension at the immigration office is the item to book the moment your course confirms enrolment; it has a queue and it is the thing standing between your initial 90 days and the rest of your course.
Days 20–30: set the clock running. Start a day-count log on day one of arrival — not day thirty, when you have already lost track. Tax residency starts at more than 180 days in a calendar year, and if you are on a DTV planning to use the 180-day stay plus its 180-day extension, you will cross that line inside the first year. Diarise your visa expiry and any extension window with two reminders, one at 60 days out and one at 30. Then, and only then, buy the motorbike, join the gym, and start saying yes to things.