Gary, start by checking out the beaches close to the Haulover cut rock wall, the south inner part of the cut (Bal Harbour side) has a nice beach area surrended by rocks and the waters are calm, stay away from the inner side of the canal as there are lots of powerboats coming in and out.
Another good place to go snorkeling is Red reef, this is north of fort lauderdale in the area of Boca Raton.
The ultimate ofcourse is to go on a snorkeling tour of penne camp in Key Largo, they provide the equipment you just pay like $40 for everything.