Only take official White Taxis from FCO. The fare is fixed at €55—confirm this with the driver by asking "Tariffa fissa?" before you leave. Skip the Leonardo Express if you’re tired; instead, take the FL1 regional train to Stazione Trastevere (€8) and then hop on Tram 8 to Arenula/Cairoli. It brings you right to the neighborhood edge without the Termini madness. (Keep in mind the FL1 is not the more obvious Leonardo Express, and the airport train station is located over by Terminal 3.)
Need to hit Termini? Take Bus 40 Express from Corso Vittorio. It’s fast, cheap (€1.50), and way better than the Metro. Just tap your card on the bus.
The closest taxi station is on the far side of Campo de' Fiori at Piazza di San Pantaleo. The next closest taxi stand is at Largo di Torre Argentina. Uber does exist in Rome but may take much longer than a cab; Uber may be cheaper than a cab, but that is not guaranteed.
Set up your account and install the app before riding, and start the ride directly through the app. Scooters and e-bikes can be fun and convenient, but they are expensive and dangerous. Avoid crowds and fast traffic, and be careful on cobblestones and hills.
You can buy paper bus tickets (€1.50) at all tabacchi stores (tobacco shops, signaled by a white 'T' against a black background) and at the hexagonal green tourist shop / newspaper stands found in most piazzas. You have to validate your paper ticket in the machine on the bus or pay by card (note that not all cards work with tap to pay). They check for validated tickets on the bus and will fine you.
Standard train tickets need to be validated by using the validation machine at the station before boarding the train. If you purchase an e-ticket that has a barcode, you do not need to validate it. If you sit in the wrong seat/car on the train, you will be fined.
Pay attention to your stop: trains coming from the north will stop at Tiburtina before Termini.
Take photos of the car from every angle (front, back, left, right, roof, and each of the four corners) before leaving the lot. Having timestamped close-up photos at pick-up is necessary to avoid return fines.
They do not appear to limit liquid container sizes in carry-on luggage and do not ask for identification on domestic flights within Italy.
For granular maps and every way to reach the pad (including the "Smart Commuter" route):
Which Renaissance bridge connects Regola to Trastevere?
Answer: A - Ponte Sisto.
Built by Pope Sixtus IV for the Jubilee of 1475, it is one of the most iconic and photographed bridges in Rome.