To get to the city you can take a bus or cab. The bus stop is 20 meters from the exit of the arrival terminal. The trip takes about 40 minutes and costs 3,20 EUR per person.
The ΚΤΕL bus schedule can be found on the carrier's website. In season, there are 5 flights per day (first at 7:55 and last at 19:40), out of season the airport bus runs twice - at 13:00 and 20:30.
A second option is to take a cab (the parking lot is located next to the bus stop). It will take about 20 minutes to get to the city center, so expect to pay 30-35 EUR. Cabs can be difficult to get in season due to the influx of tourists, so it's best to order or book a cab in advance.
For example, on the site you can book a cab at a fixed price (regardless of plane delays) and negotiate individual requests (a driver with a sign with your name on it will meet you at the terminal exit).