Getting around South Beach is easy. Parking in South Beach is the hardest practical problem a visitor faces here, and the two facts are related: the island is small enough to walk, which is exactly why there is nowhere to leave a car.
The geography explains it. This is a barrier island a mile and a half long and under a mile wide, with a resident population that lives on the same twenty-three blocks the visitors want, a hotel row with no off-street parking of its own because the buildings went up in the 1930s, and a nightlife district that generates demand at two in the morning. Miami Beach responded with one of the more aggressive parking regimes in Florida: metered on-street parking at $4.00 an hour in the South Beach core, enforcement until 3am rather than 6pm, round-the-clock enforcement in the Entertainment District, residential permit zones that begin one block off the commercial streets, and a tow operation that is not a rumour.
So the first decision of your trip is not which route to drive. It is whether to have a car on this island at all.
For a trip centred on South Beach the answer is usually no. You can walk from the sand at 10th Street to the bay at Sunset Harbour in about twenty minutes. The city trolley is free, runs the length of South Beach roughly every twenty minutes, and covers the streets you actually use. Rideshare to the mainland is straightforward. A rental car earns its keep for the Everglades, Key Biscayne or a drive down the Keys, and for nothing else. Many visitors are better off renting for one day in the middle of a week than for the whole week.
If you are driving anyway, whether because you live in Florida, because you came down the coast or because the rental was part of a package, the rest of this page is the part that saves you money. The short version: park once, in a city garage, on the western side of the island, and walk. The daily maximum in the city garages is $20, which is less than three hours at a meter and roughly half of one hotel valet. One garage, at 5th and Alton, gives the first two hours free.
What follows is where those garages are, what the meters cost by zone, how the permit zones and the tow work, where the free trolley goes, and how to get on and off the island without the causeway ruining your evening.