Flights arrive at Marco Polo Airport (VCE), on the edge of the lagoon about 12 kilometres from the city. From there, the most atmospheric way in is by Alilaguna water bus — the Orange Line goes directly to the Grand Canal, takes about 70 minutes, and costs around €15. The ATVO or ACTV bus to Piazzale Roma is quicker (25 minutes) and cheaper (around €8), from where you walk into Venice or take a vaporetto. Water taxis are fast and expensive — around €110 for the transfer to San Marco.
By train, Venice Santa Lucia station sits right on the island at the western end of the Grand Canal. Direct Trenitalia and Italo services connect it to Milan (2.5 hours), Rome (3.5 hours via high-speed), Bologna (1.5 hours), Florence (2 hours), and Verona (1 hour). The station name matters: you want Santa Lucia, not Venezia Mestre, which is on the mainland.
By car: you can drive as far as Piazzale Roma or the Tronchetto car park on an artificial island at the western edge of Venice. Parking is expensive (from €25 per day). There is no driving inside Venice. Tronchetto has a shuttle bus and vaporetto connections. Most visitors find it less stressful to park at Mestre on the mainland and take the train across the lagoon causeway (10 minutes).