Airport pickup service is available either through the booths of the various car rental companies, or through complimentary services of a hotel that you may have booked a room in.
Otherwise, taxis are always available to take you to your required destination. The exact fare from the airport to the downtown area is $38.
There is also a commuter train station near the airport - the train is ideal if you arrive at the airport during road rush hours, as it takes a diversion from the main roads to the city center. Do check the schedule for the departure time, as it may sometimes be more time-saving to hit the road instead.
A shuttle bus (Aerobus) runs between the airport and the downtown district, costing $15 per ticket, with discounts for children and elders. Stops at some hotels along the way.