Pack camping gear loosely if possible. Border agents may want to check what you are bringing in and out of the country.
Bring bottled water. Most water in the town should be filtered, but you'll want to play it safe while staying at the beach. In other words, do not drink from fountains or taps.
Get to the beach early in the day, on weekends or first light during a high-tourist season like spring break.
Search for beaches where tent camping is available. There may or may not be signs posted so ask an official.
Park vehicles about 100 yards away from the beach in designated overnight parking areas. Carry backpacks and gear to the campsite. Some beaches allow cars, others do not.
Drive to an RV campsite. Most can't be missed--they're huge cement slabs that don't look much different from parking lots. Signs will be posted that designate these sites.