You can easily get to Venice by car through motorway (A4 from Trieste and Turin, A27 from Belluno, and A13 from Bologna) and road links (highways SS.309 Romea from the Adriatic coast, SS.14 from Trieste, SS.13 from Treviso, and SS.11 from Padua). Once you’ve reached the lagoon take the Ponte della Libertà, the bridge that literally links Venice to the mainland. If you follow the signs to Venice you’ll find yourself in Piazzale Roma, which is as far as you can go by car. Here you have to park your car.
In the Piazzale Roma area the following parking garages are available: Autorimessa Comunale, Garage S. Marco and S. Andrea. There is also a large parking lot on the Tronchetto island (turn right at the end of the bridge). However, another possible solution is to leave your car in Mestre (either in the parking lots by the entrance to the Ponte della Libertà or the ones near the Mestre railway station, which are definitely cheaper) and continue from there by bus or train to Venice.
If you are staying in Mestre it will be better to leave your car near your hotel and get to Venice by bus. There is a bus about every 10 minutes. At night connections are less frequent but you can still count on them. The bus fare is 1 Euro. If you prefer to park in Venice, the best solution is to park on the Tronchetto island: at the end of the long bridge (Ponte della Libertà) that links Mestre to Venice, turn right at the first traffic light, then follow the directions. The garage will charge you 22€ a day (even if you park there for fewer hours). If you prefer to park closer to the centre, go to Piazzale Roma (the only square of Venice that can be reached by bus or by car). To get there, go straight (don’t turn right at the traffic light): you will find three garages. From here you can take a vaporetto (check the price on the relevant page).