By train
Rail travel in Portugal is usually slightly faster than travel by bus, but services are less frequent and cost more. The immediate areas surrounding Lisbon and Porto are reasonably well-served by suburban rail services.
The rail connections between the main line of Portugal, i.e. between Braga and Faro are good. The Alfa-Pendular fast trains are comfortable, first class is excellent. The Alfa-Pendular train stops only at main cities stations and often requires advance reservations,recommended between Braga, Porto, Gaia, Aveiro, Coimbra, Lisbon and Faro.
Intercity trains will take you to further destinations, specially in the interior, such as Ãvora, Beja and Guarda.
By car
Traffic in Portugal is done on right-hand side of the road.
Roads are generally good, and you can reach all major cities with ease, either by motorway or by good, modern roads. The biggest cities are well served by modern highways most have tolls, and you can travel the full North-South length of the country without ever leaving the highway, if you choose to.
However, some secondary roads are ill-treated and may be dangerous if proper care is not taken. Also, Portuguese driving can seem erratic and, frankly, scary to the uninitiated. The country shares with most southern European countries something that the successive Portuguese governments have been trying to fight: terrible road behaviour from some drivers. In order to fight this, road laws changed recently in order to punish with great severity speeding, driving without license, driving under the influence of alcohol or narcotics, etc.
The motorways with the most reckless driving are those 50 km around Lisbon or Porto, the A1 and A2 and the Algarve.
You can be on a 2-lane toll highway and be unable to see any other traffic except the car you're overtaking at 30 kph over the speed limit and the car about 6 feet from your back end flashing its headlights to get past you. Merging manners when slip roads come on to fast roads are also pretty poor. On other roads, you'll get used to two classic Portuguese experiences: suicidal overtaking attempts and the resultant absurdly overdone signs indicating when you can and can't overtake - sometimes all of 5 yards apart, and the "penalty stop" traffic light as you enter the 50 kph zone in each small town, with camera to decide whether you're over the speed limit. Rather absurdly, once you're through this, your speed isn't checked again.
It is probably unwise for those unfamiliar with Portuguese driving to try to drive in Lisbon or Porto - be aware if you do that city drivers give no quarter and have limited respect for lane markings where lane markings exists!. If you do want to try, choose a weekend or an hour outside the rush hour periods. These are early mornings 8AM - 9.30AM and late afternoons 5PM - 7.30PM. Other Portuguese cities are much better, but often have very narrow roads.
By bus
Unfortunately the rail network is limited, so you may find yourself busing about to get anywhere off the beaten path. Rede Expresso (http://www.rede-expressos.pt) is one of the largest inter-city bus companies.
Lisbon and Porto, the two largest urban cities, have a clean modern and air-conditioned metro systems underground/subway and light railway.
Road traffic in Lisbon and Porto is pretty congested all day round and gets completely stuck in the rush hours, at least in the main roads to exit or enter the city. Car travel is the most convenient or only method to reach areas outside the main cities, however car rental is not too expensive, but the associated insurance is - unless you book the total package abroad. Heed the advice about the quality of some people's driving skills mentioned below.
Generally speaking, Portugal is not a good country for hitchhiking. In the deserted country roads in the South, you might wait for many hours before you are offered a ride. Try to speak with people on gas stations or parking lots etc. Drivers tend to be suspicious, but when you show them that they should not be afraid, they will probably accept you and mostly also show their generosity. Try to look neat and clean. The hippy style will get you nowhere. As with everywhere in the world, two males hitchiking together will not get a ride from anyone.