When most people think of Miami Beach, they're envisioning South Beach (SoBe). This area is rife with clubs, bars, restaurants, models and a distinctive veneer of Art Deco architecture. The beach itself encompasses a lovely stretch of golden sands, dotted with colorful deco-style lifeguard stations. The shore gathers a wide mix of humanity, including suntanned locals and plenty of tourists, and gets crowded in high season (December to March) and on weekends when the weather is warm.
You can escape the masses by avoiding the densest parts of the beach (5th to 15th Sts). Keep in mind that there's no alcohol (or pets) allowed on the beach.