Wow, where to begin? What do you like to do? How old are you? Where will you be staying?

South Beach is of course famous. Beaches there are nice and for women, tops are optional.
Strolling down Lincoln avenue for shopping and food.
Lunch or drinks at the Clevelander on Ocean ave is required.
Nightlife on Washington is great, especially if you are younger.

You want to try Cuban Coffee or Cafe con leche and a visit to a Cuban restuarant is a good choice. My favorite is Los Rancheros.

Any of the water tours out of Bayside, next to the American Airlines Arena are touristy, but you get to see lots of celeb homes.

Coconut Grove has good shopping and food.
Vizcaya is a great place to tour if you like museums.

Let me know what you like and I can better send you in the right direction.