MIA: the approved spotting holes are just east of the Customs Cargo Clearance Center which is on NW 25th Street and just north of the two FAA control towers. Don't park in the Customs lot or you will meet some real a-holes. This location is on the west side of MIA and you can reach NW 25th Street from NW 72nd Avenue (Milam Dairy Road), the Palmetto Expressway (State Road 826), or from the north on Perimeter Road which goes around the northwest corner of the airport just south of NW 36th Street. If you get a decent map you should be able to see what I'm talking about.
FLL: take the Griffin Road exit off of I-95, go west to the first light (can't remember the name of the road - Ravenswood?), make a right (north) until the next light. There are signs saying "General Aviation" or something like that. Make a right (east), go up and over the bridge over I-95 and you'll come to a 4-way stop at the bottom. Make a left (north) and go to the next stop sign. Make a left (west) and follow the road up to I95 fenceline and then it curves right (north) and the viewpark will be on your right. You'll be just south of the approach end of 9-left.
Photographing aircraft since the Earth was flat and on Airliners.net since #338