I live and go to school in North Miami/ Miami Shores and usually just go out around there because it's tons cheaper. I don't really like the club scene... I prefer laid back bars (Ale House, Flanigan's, etc). I'm in college where it's easy to meet women, though. When I go to the bars, I'm there more just to relax, have beers, and watch sports.
If you're out of school, you will have to hit the clubs to find most of the really hot women. I do hit South Beach occasionally, but not very often. It's mainly where a lot of tourists or really rich people go to party. Between the cover charges and the drinks, that gets damn expen$ive, though. I'd highly recommend "pregaming" at home so you don't have to buy ten tiny $15 drinks or a couple $300 bottles at the clubs.
For South Beach, Mansion's probably the best club; you'll see some celebrities and other cool stuff there. The girls are off the charts, but they'll be expeting drinks all night. If you don't make six figures, I've found it hard to pick up the really fine Paris Hilton wannabe girls there.
To save some cash, Lucky Strikes bowling alley is also a laid back and decent place to go with a big group or to meet girls. It's in south beach too. It's a bar too and the place gets really packed on weekends (reserve lanes if you go Fri or Sat).
If you go downtown, Metropolis is worth checking out... good club but not quite as expensive as SB.
Hollywood Hard Rock Casino is pretty far from where you're at, but there's a few good dance clubs there too if you want to change it up (Passion, Gryphon, etc). Spendy, but not as bad as SB either.