As far as freedom of movement and exploration a car can be invaluable. Though small the island's tightly turning mountain roads make for relatively long journeys and a hair-raising experience. Driving is on the left hand side of the road and there are various car rental agencies at both airports.
Honk horn on hairpin turns especially during the day.
Beware of large lorries as their width forces other drivers off the road.
Watch for large pot holes and crumbling asphalt as roads can be in very poor condition.
Ask directions if lost, the locals are very friendly and informative.
When in mountains in torrential rains, consider stopping for a bit or at least going very slowly.
A compact is sufficient for most situations but a small 4x4 might also be nice. A large 4x4 would be cumbersome on the small streets.
Other travel options include buses. If you are on a low budget and have plenty of time then the bus will be fine except on Sundays, or weekdays after the early evening, when the only bus running goes between Portsmouth and Roseau, although sitting in a bumpy bus for long trips on winding mountain roads is not the most comfortable thing to do. However, these buses are generally safe and timely; the local drivers know the roads well and are used to all the usual weather conditions. Buses are owned and operated privately and therefore do not have to adhere to any timetables and come and go whenever they are filled to the driver's satisfaction– ask around for approximate departure and arrival times, but know that they vary day to day. Most villages have three to ten buses Portsmouth is the primary exception– it has dozens, possibly hundreds, of buses that perpetually shuttle passengers to and from Roseau that go to Roseau or Portsmouth, if they are from a village in the far north– ask the driver, though most of the buses that are advertised as terminating in Portsmouth actually will go all the way down to Roseau, operating as service from Portsmouth to Roseau in the morning to drop off students or employees, and return in the afternoon with these same people returning home. In Roseau, all villages have designated bus stops that may or may not be marked by a large, red sign. Whether they are marked or not, all shopkeepers and pedestrians you are likely to encounter know the exact location of the stop for your destination. In stark contrast, in the villages, where there is only one bus route to and from Roseau, or Portsmouth, buses leave from the owner's garage and tend to drive aimlessly around town until the drivers have collected enough money from bus fares to make the trip profitable. However, when they drive around town, they oftentimes circle back to a shelter, awning, or public area that the locals refer to as "the bus stop." Occasionally, they'll just remain stationary there.
If they are not full they usually are, buses will pick people up anywhere along their route, so long as they can feasibly pull over and let them onboard. Generally, there are shelters along the routes, either in towns that the bus passes through or at major intersections, where hitchhikers gather. If this shelter is along a bus route, you may get lucky and a bus with an empty seat will stop for you. Be prepared for some competition in claiming this seat. Likewise, buses stop anywhere within reason along their route. Though the hitchhiking shelters are preferred, asking the driver to stop will usually net an opportunity to get out whether there is a shelter there or not.
When taking the bus, remember:
Keep an eye on your belongings. Dominica is highly safe and crime is minimal, but there are pickpockets everywhere.
Don't overpay. The only thing about these buses that are regulated by the government are the fares. Ask the other passengers what they paid; upon seeing a foreigner, the operator may try to squeeze some extra money from you.
Ask the locals about the bus. Buses from every village operate somewhat differently in terms of trip duration, departure and arrival times, pickup points, and the location of their stop in Roseau.
Be prepared. Taking the bus is quite the experience; you will oftentimes be packed in like a sardine, and those that don't like to be touched which is inevitable on a Dominican bus or are claustrophobic should consider hiring a car.
Don't complain about the music on the radio, the close quarters, or any uncomfortable seating arrangements you find yourself in. Not only will the driver take personal offense to this it's his personal car, but he usually won't do anything about what you say. Plus, the other passengers tend to laugh at you.
Know a real bus from a fraud. All licensed taxi and bus operators drive vehicles have license plates that start with the letter H.
Get on early. Before they go, buses will wait either at their designated spot in Roseau, or somewhere in town when leaving from another town to fill up. The best seats are usually the first to go, so grab them before somebody else does.
Talk! Foreigners don't tend to take the bus, so your fellow passengers will inevitably be curious. Don't force conversation, but answer questions politely and follow them up with questions or comments of your own.
Taxi is more comfortable than the buses and may not be expensive, particularly if the fare is shared with 2+ travelers. Whether you use the bus or taxi, make sure that you clearly agree to the destination and price before you start the trip.