If you land at Pisa Airport, the hotel where you booked your room will most likely provide a shuttle service. You can also get to Viareggio by train from Pisa Rossore station. From the airport you can get to the train station by a LAN Rossa bus operated by CPT every 10 to 20 minutes (from 5:20 to 00:01 on weekdays and from 7:25 to 00:01 on weekends). Electric trains go every half hour and the ticket price to Viareggio varies from 3.50 EUR (during the day) to 9.50 EUR (at night). The whole trip takes about 30 minutes.
The airport itself is located 1 km from the main railway station of Pisa (Stazione Pisa Centrale), where you can get to any major point of the country. For more information - timetables, fares, purchase - visit trenitalia.com.
The airport is connected to Pisa by the Red LAM Line bus line. The route goes through the railway station, Piazza Vittorio Emanuele, and the Santa Chiara Hospital. The ticket costs 1,20 € and you can buy it at the information desk or at the terminal at the stop at the exit of the arrivals area. For more information, timetable, cost, and purchase, visit pisa.cttnord.it.
You can also take a cab at the exit of the airport terminal and in 20-30 minutes you will reach Viareggio for about 35€.