Get the motorway SGC Firenze-Pisa-Livorno towards Florence, then follow indications to the city center.
At the stop "Castelpulci", take bus number 15 and get off at "De Andre" stop, then take the tram towards the city center. or At the stop "Castelpulci", take bus number 72 and get off at "Nenni", then at the stop "Federiga" take the tram towards the city center.