The general wisdom for planning your Jamaica travel is: "Make a plan, gotta wipe." Stay loose and soon come!
Kingston Airport and Customs:
On your customs form, you are traveling for pleasure and have no gifts and nothing to declare. You need a hotel address where you will be staying to fill out the forms. Do not lose the little part that they take off and give to you. You need it to get back out of Jamaica.
When you get to Jamaica you will go into a large room and stand for awhile in lines for immigration. In this room there is a tourist info desk and you can get a free map (if they are not out).
After immigration you proceed to get your luggage and go thru customs. Inside this large room is a money changing window and it is quite handy to have some Jamaican money when you leave this room, and you will leave this room, when you clear customs. You cannot stop and wait for others they demand you go out.
When you go outside you will walk into a large throng of people and this can be uncomfortable. They will be taxi drivers who can be very aggressive to get you to go with them. Contract with a JUTA driver here or look for Mokko with a sign saying "Riverside Cool Cottages", or Free-I with a sign that says "Zion Country", depending on what arrangements you have made.
Taxis with a red plate are official "route taxis". They travel on a certain route and are very cheap. If you ask a taxi to go to a specific place just for you, the price goes up and it is now a "charter taxi". Taxi drivers are licensed, strongly regulated and incredible drivers. Grab on, close your eyes if you wish, and trust these drivers. This is where Nascar Drivers are trained. Consider using this
US cell phones do not work in Jamaica. But everyone has a cell phone. So if you buy a phone card in Jamaica (usually $130 JD) you can borrow someone's phone to make local calls or call home inexpensively. Leave extra minutes on the phone and the lender will be very happy.
Cashing money can be done at the airport, in the big towns at banks, cambios and FX trader locations. The airport exchange rates are about $5 JD/$1 US less than the other locations. There are ATMs in the big cities only. Few places accept US dollars in the countryside, though you can pay with US$ at Zion Country. Exchange rates in November, 2008 are $75 JD/$1 US at the FX Trader (both Morant Bay and Port Antonio has one).
So far, all monetary transactions we know of involving "helpful" people on the streets turned out to be rip-offs.
You can access the internet from the local libraries in Morant Bay, Long Bay, and Port Antonio. There are several internet cafes in Port Antonio which work well for a small price ($50 JD/1/2 hour), one is located across the street from Kamaals Supermarket and one in the pink building across from the Marina. Both have good service.
Mokko suggests that you keep your business private in taxis and public, carry small money in one pocket and no big bills in that pocket.
If you carry any agricultural products, be sure to declare them. What is allowed into our country changes frequently and often we are suprised about what is allowed. But if you do not declare the products, you could get a stiff fine if the items are found. Don't ask how I know!
Kris has posted a Jamaica Starter Kit with excellant information about getting to and around the island.