Miami And Miami Beach are actually two different cities bridged by four major causeways over Biscayne Bay and the Intracoastal Waterway.
The first thing to know about the city of Miami is that it is divided into four quadrants NW, NE, SE, and SW. Most all streets east and west are numbered, which can be confusing if you don't know what quadrant you are in. For the inexperienced, a map is a necessity.
Miami Beach streets are very easy to navigate, with 3 major roads (Ocean Drive, Collins Ave., and Washington) running North and South. The streets running east west are numbered. The quickest way over to the beaches on the north end is I-95- which is 6 lanes wide and dumps you north of the Art Deco Historic District on 41st Street. The southern access is I-395, commonly called the MacArthur Causeway. This sends you onto 5th street, the southern end of South Beach.