In Portugal, driving is on the right with overtaking on the left and you can be fined more than 1,000 Euros if you pass a driver on the right. On the motorways there are three lanes with the middle one being for overtaking.
At night in rural areas look out for horse drawn carts. When a tram stops and there is no island for passengers to disembark at, drivers must give way to them. Avoiding rush hour traffic in the cities is to be advised.
It is safest to drive defensively in Portugal, which has one of the less impressive driving safety records in Europe. You can find interactive online maps of the country at http://www.travelportal.info/western-europe/portugal/maps.