Most trips to Amalfi are done by boat, commonly people use Naples as a transit point, but you can also take ferries from Capri, Salerno and Paestum during the summer months. If you get easily sea sick, or would just rather take the bus, there are regular services by Sita Coach to Amalfi 1h50 (http://www.sitabus.it) about 4 times per day.
Taking your car is discouraged because of the road size and lack of parking. During the summer there may be limitations on the road for tourist buses: e.g. sometimes the road along the coast is one way only for tourism buses from Sorrento to Salerno.
