Delft is exceptionally well-connected by train. Direct services run to Rotterdam (12 minutes), The Hague (10 minutes), and Amsterdam (about 1 hour). Both Rotterdam Centraal and Amsterdam Centraal have Intercity and Sprinter connections to Delft station throughout the day and evening. The train is comfortably the best way to arrive.
Delft Station itself was rebuilt underground in 2015, with the former railway tracks replaced by a beautiful new urban boulevard running through the centre of the city. The station building, designed by Mecanoo, has become an architectural attraction in its own right: a sloping glass facade etched with Delftware-style blue patterns and a vaulted interior.
By road, Delft sits on the A13 motorway between Rotterdam and The Hague. Parking in the city centre is limited and expensive — arrive by train if at all possible. Schiphol Airport is about 50 minutes by train.