Hiring a car or jeep is a great way to explore the island, but just a few tips to make the experience a little less fraught than when I did it the first few times.
Drive on the left hand side - this is fine for a Brit like me, but there's an added point of interest in that most of the cars are imported from the US, where there are right hand drive, which makes life a bit trickier.
The roads are in pretty poor shapes in some places, so watch out for pot holes.
Some of the hire cars may have poor suspension, which means you have to be even more careful with those potholes. We hired a couple of supposed 4 whell drive vehicles which were pretty lacking in the suspension and power departments.
Some locations really do need a proper 4WD to get to safely, eg. Levera beach and some places on the east coast. If it's been raining you will have real problems in some places, and with no fences at the side of the road it could be quite dangerous. We had a few lucky escapes.
Driving up across the rainforest is great fun, but the roads are very narrow and winding. The local buses are kings of these paths so expect one at every bend and creeping onto your side of the road. Avoid driving though rainforest roads at night of if it's raining.
I've learnt all this by my own mistakes, so enjoy the island, but be careful!