I live in Miami and have learned from my mistakes both before and after I moved here. Miami is loaded with gimmicky restaurants and loads of general tourist traps. These are just my opinions, but I don't think many people will disagree. Here is how you can visit Miami and not act like a tourist.
Avoid South Beach between 5th and 23rd
If you're visiting Miami for the first time, you're probably going to stay in South Beach, and why not? You'll be close to a beautiful beach with plenty to eat and drink at your disposal. It sounds like a perfect place to be apart from the bad food, overpriced sugary drinks, and crazy tourists. There is plenty wrong with this area.
Instead: Visit South of Fifth, Mid-Beach, Brickell, Coconut Grove, Wynwood, Coral Gables.
Avoid Bayside Marketplace
Bayside Marketplace is an outdoor shopping center right on the Biscayne Bay. It is the most visited attraction in Miami, even more reason to avoid it. Every cruise ship that stops in Miami has shuttles to drop cruisers at Bayside Marketplace, hence why it's the #1 attraction. Here you'll find crowded shopping, lower quality food, and overall mayhem. You can also hop on a charter boat for a booze cruise or high-speed boat tour, which would be cool if the service wasn't horrible.
Instead: Check out Brickell City Centre. It'll be a bit more expensive, but far nicer and better-quality food and merchandise. No boats for hire here though.
Avoid any Surf Style, Wings Beachwear, or Alvin's Island
All three of these appear to be super cool and trendy "surf shops", but they're not. They're stores with thousands of overpriced items and the size of the store will trap you for at least 30-60 minutes. I made the mistake of going into a Surf Style when I first came to South Beach. There is a Surf Style on almost every block along Collins Ave and I thought I'd be able to find a cool tank top or surf gear. Wrong. Even if you're just looking for Miami souvenirs, look elsewhere.
Instead: For souvenirs, check out the Official Art Deco Gift Shop. For surf gear, check out South Beach Dive and Surf Center.