Despite its small size, Pisa is extremely accessible by land and air, so you should have little trouble getting here.
Pisa Airport (officially the Pisa Galileo Galilei Airport) is the largest in Tuscany and feeds into Florence and Pisa, as well as neighboring areas of Tuscany. You can fly here from all over the world, but you may have to transfer from another nearby airport if there aren’t any direct options.
While it’s technically feasible to walk from the airport to the city, that’s a ridiculous idea when you’ve got a load of bags. The is as cheap as any normal ticket (€1.30 for an hour) which is more than ample to get you into the centre, and can be bought from the information desk as soon as you’re in Arrivals. From there you can probably walk to your accommodation, but taxis are readily available if you’d rather not.
You can also travel from the airport directly in a taxi, which might be easier if your accommodation isn’t near the train and bus station. It will probably cost under €10 if you can share with a few others most of the way.
Situated in central Italy, it is very well-connected to the rest of the mediterranean by train. Services to/from Florence are extremely frequent (several per hour) as well as connection to major cities like Rome and even Paris. Though you can get away with hopping on a train without a ticket in some countries, this won’t fly in Italy - make sure you buy a ticket, even if it’s just a short jaunt over from Florence.
As a tourist, you only ever need to walk to get from A to B; as a local, you’ll probably explore the surrounding area, nearby towns and suburbs much more thoroughly, so investing in the City Bikes subscription or using the buses is advisable. The city is very easy to navigate given its size, and buses can take you on any long journeys.
Large parts of Pisa are paved and designed to accommodate cyclists, and its popularity is on the rise. The Ciclopi City Bike system is good, but there are only 200 bikes, meaning you might struggle to find one nearby on a busy day. It’s worth looking online and buying a second-hand bike of your own, since you’re likely to use it daily!
If you don’t want to invest, it’s only €25 per year for the Ciclopi subscription, giving you unlimited half-hour journeys on the bikes.
There isn’t a subway or tram system, since the city really doesn’t require one - it’s too small. You can walk and cycle your way through the city centre, but the bus service is there for any longer journeys, or for when it’s raining and you don’t want to get soaked. Tickets cost €1.30 for a single, which lasts an hour. If you need more than 60 minutes for a single journey around Pisa, you’re doing it wrong!
Of course if you drive to the city and want to explore by car, that’s the obvious choice! Just remember that the historic centre of Pisa is a car-free zone, so you won’t be able to drive there at all. If you get accommodation outside the centre, there is plenty of free parking nearby so your car could still come in very handy!