Arriving by train at Santa Maria Novella station you are close to the city center. Many hotels are located nearby the train station or are walking distance from there .Many visitors will wheel small suitcases along the pavements but this is not recommended if your case is a full 20k as the streets and roads are mostly uneven.  If you take a taxi from there you can reach every area of the city center for less than 10 euro. The meter may show less than that, but there is a charge for luggage.

Arriving by bus from Pisa airport also drops you on the Western side of Novella station. To get a taxi you go to  the western side of the train station (on the left facing the station from across the street) and make the line. Or take a local bus if you have only a backpack. Therre is a map of bus routes in Florence. The Bus tickets are purchased at any Tabacheria inside the station and MUST be validated upon entering the bus in the machine for that purpose. Tickets are good for 90 mins, enabling you to change buses . Florence is linked to many locations via Italy's excellent railway services, but the Inter-Citybus services (SITA and LAZZI) are equally good, with frequent service at much the same price If you go to Sienna by train you have a long uphill walk from the station. The bus depot is near the heart of the old city..

Arriving by car you have several options:

Arriving from NORTH or WEST take the motorway exit "Firenze Nord"

Arriving from SOUTH (ROME) take the motorway exit "Firenze Sud"

Arriving from SOUTH (SIENA) take the motorway exit "Firenze Certosa"

Bear in mind that the heart of town is off-limits to private vehicles (ZTL - Zona Traffica Limitata), but your hotel will register your car asking for the number plate upon your arrival. Ask for specific directions.  Take  special care not to pass over the Bus only restricted streets. In that case, the registration in the hotel can't cancel the penalty.  Be careful with rental cars - if you are not going to your hotel or the rental car agency to return it, you may find a 70 euro fine on your credit card (from the police to the rental agency to you) later on.  You then owe it.