In Greece you'll drive on the right with overtaking on the left. You must always give way to the right when you approach a junction. Care should be taken especially on left turns as following vehicles may be trying to overtake you at the same time! Driving defensively is also a good idea. Watch out for people who cut lanes and cut corners.
On the three lane highways the middle lane is used for passing. Don't obstruct the fast lane. Take care when driving on Greek roads as the quality can vary greatly. In some of the most beautiful places paved roads will give way to gravel roads and so your speed should be adjusted accordingly. Greece also has a high proportion of accidents compared to other European countries. Some of the most dangerous areas are the single lane mountain roads where you have to pass into the oncoming lane of traffic to overtake. Most petrol stations are open for twelve hours between 7am and 7pm but closed on Sundays.
By law one petrol station per area should remain open at night and on Sundays so if you are low on gas out of hours get a local to direct you to that petrol station. In Greece there is a system of heavy fines of hundreds and even thousands of Euros for the following offences: running a red light, crossing a double white line, not stopping at a stop sign, talking on a mobile and parking illegally on a national road so it pays to follow the rules meticulously.