When I say "club DJ" I don't just mean dark wave or oontz, I mean DJs of all genres and styles of music. Today's technology makes it so anyone with a laptop and a RCA Y-cable can plug into a sound system and be a DJ, but what sets the names that are in demand apart from those who just play their iTunes playlist?
I think one of the more important aspects is knowing the genre you're playing. Whether it's club retro 80's or low-country honky tonk rock 'n' roll, if you don't know the genre you're not going to make it. If someone comes up during a swing/jive night and requests Morrissey, your ass is grass and the audience is going to be the lawn mower. There are subtle differences between industrial and techno that cause cause you to win or lose your audience with just one wrong song. Perhaps, pick a genre to "specialize" in - maybe something you know is fairly popular and would gain you some attention. This way, you can really delve into the history of a genre and become a "master."
You also need to know how to read and work a crowd. Playing party tune after party tune will not go as well as you might think. Recognize when your audience wants something more upbeat, or if you've been playing songs at 200 BPM it might be time to slow it down and let them catch their breath. If nobody is dancing, try changing the beat, style, or even decade you're pulling music from.
Your equipment also plays a big role in taking things from backyard gatherings to rocking a dance floor full of swing dancers. When I say I'm a DJ, some of my friends and acquaintances frown at me because I don't spin vinyl. I may not have 200lbs of vinyl records to lug around, but I DO come packed with over 15,000 songs ready and available to play at a moment's notice from my laptop. Speaking of laptops, don't depend on using iTunes or Media Player to play your music. That's the loser approach! Spend a few dollars and install an application that'll fulfill your needs. I use and recommend djay - it's a fairly inexpensive app available for Apple devices.
Follow the above and it'll get you on the path of where you want to go. Be yourself, be unique, learn a few things, and experiment. Find out what works for you.