If you don't have skates with you you can rent them from Fritz's on Lincoln Road. You can skate all over Miami Beach but the best area is on South Beach as described earlier. It is just gorgeous to skate along next to the beautiful water watching cruise boats, and sailboats glide by. Turn to the street side and you will see all kinds of gorgeous people skating with and around you.
You always seem to have the tropical breezes on Sout Beach so you can get a good workout but you won't be sweating everybody up...lol. Have fun!