You can reach Sardinia by plane (the easiest and faster way) or by ferry.

By plane.

The closest airport is Cagliari Elmas - http://www.sogaer.it/ - (90 mins drive) but there are two more airports on the island: Olbia and Alghero.
Many direct flights and low cost carriers are available from Italian and foreign airports.
Please remember Sardinia is a sought-after destination in the summer – book early for the best deals!

By ferry.

Several companies offer both day and nightime ferry crossings to various ports in Sardinia:

Tirrenia - www.tirrenia.it

Moby Lines -www.mobylines.it
 
Sardinia Ferries – www.corsica-ferries.it