Most of the population and hence shopping, food and entertainment is located along the "East-West Corridor" which is the set of cities and towns along the main routes of transport. It starts in the West with the capital Port of Spain and ends at Arima. Transport is easy attained along these routes.
By car
There are numerous possibilities for hiring cars in Trinidad, and this can provide a cheap way of getting around, as petrol is so cheap. Aside from the rather erractic driving of many of the locals, the main problem with getting about like this is that the road signs tend to be rather sporadic and inconsistent, and there don't appear to be any good maps available. As a result, you need to be prepared to spend rather a lot of time getting lost.
Econo Car Rentals Ltd. - they are the cheapest, with cars available from $30USD per day. The service is friendly and reasonably efficient. Bear in mind though that you will need a valid credit card and be over the age of 25 in order to book with them.
Taxis
Taxis are hired at 'taxi stands' which are located in every major town, and other popular destinations. Legitimate taxi license plates always start with an 'H' for 'Hire'. Taxis, for the most part, drive along a fixed route. The exception is for taxis which take passengers into neighborhoods, in which case you must inform the driver of the destination street. Expect the driver to wait until the taxi is full usually four passengers before leaving, so you might have a long wait at quiet hours. Always ask the driver to make sure where the route goes, and if you are in the right taxi stand. There are usually multiple taxi stands to different destinations in close proximity. The route fees are fixed typically $3 to $5 TT, but going up to $20 TT for long routes, but ask the fare before leaving. If you don't wish to wait, or need to go off-route, negotiate with the driver and you can get the taxi all to yourself. The main advantage of taxis is that there are typically fewer stops getting there faster and you can ask the driver to place bulky packages in the trunk. A warning: air conditioning is not mandatory or typical.
Maxis
Maxis are the private mini-buses that drive along major routes, and pick up and drop passengers anywhere between. They carry 10-30 passengers. They are always painted white with horizontal stripes on the sides red, green, yellow,brown and black. The color of the stripe used to identify the route, but this is not strictly enforced. Typically, Maxis that travel the East-West corridor between Arima and Port of Spain have a red stripe, Port of Spain to Chaguanas: green. Maxis typically can be flagged along any 'Main' road any road with 'Main' in its title: Eastern Main Road, Western Main Road, etc. as well as the Priority Bus Route which runs from Arima to Port of Spain. Main road routes are usually congested and slow, but slightly cheaper. The fee depends on distance traveled, but expect to pay $3 TT minimum also known as a Short Drop. To flag a maxi, extend your arm upwards and indicate using your fingers how many passengers want to board. Ask the driver to make sure he is going where you wish to be. Passengers must press a buzzer located above their seat to indicate that they wish to disembark if stopping before the end of route. If you don't know the area, ask the driver. Some maxis particularly the larger ones employ a conductor. The conductor collects money and indicates where you should sit. He is easily identified by the wad of cash in his hand and his occasional hustling-cry to potential passengers. Air conditioning is not typical.
Public Buses
Buses are a cheap method of transport, but the waits between departures can be long. Tickets can be purchased at terminals, and are usually less than $10 TT. They are normally air-conditioned.
Private Taxi Services
These differ from 'normal' taxis which are typically individually owned and operated, in that they are owned by a taxi company and driven by hired drivers. You can call them from anywhere and they will come pick you up. These are usually nicer than 'normal' taxis: better maintained, newer and always air-conditioned. The drawback is is much higher cost expect to pay at least $100 TT.