Before you fly
Sort accommodation first. Everything else (the bank account, the address registration, in some cases the visa itself) is easier once you have a confirmed address, and arriving without one means competing for rooms in person against people who are already here.
If you are outside the EU, check your visa route before anything else. If you can, start the NIF process through a fiscal representative so the number is waiting for you.
Your first week
Get a Portuguese SIM, MEO, NOS and Vodafone all sell prepaid at the airport and in any shopping centre. Get your Navegante transport card at a metro station; the monthly pass is €40 and pays for itself in about three weeks of normal use.
If you did not get the NIF in advance, go to Finanças early in the morning with your passport and proof of address. Then open a bank account, traditional banks want the NIF and an address; digital banks are faster if you just need something working.
Your first month
Register with a health centre (centro de saúde) once you have an address and, if applicable, a social security number. EU citizens should carry their EHIC in the meantime.
Beyond the paperwork: this is the month to work out which part of the city you actually want to be in. Living somewhere for a few weeks tells you more than any amount of reading, which is a good argument for starting somewhere flexible rather than signing a twelve-month lease sight unseen.
