Miami is a big place so it would be helpful to have a specific destination. For instance, you can take a shuttle from FLL to Brightline for the trip to downtown Miami/Brickell area - one or two stops on an Acela-like modern train. TriRail is also a shuttle from the airport with slower commuter stops south, ending at MIA where as noted there are Metorail subway connections. If your destination is the beach, you're going to need a taxi/Uber at some point.