Study up on the great DJs of the past 25 years. Tiesto, Jazzy Jeff, Paul Oakenfold, Daft Punk, Girl Talk, Justice, Fatboy Slim and Mix-Master Mike all made big names for themselves by creating unique sounds of their own that built on the styles of DJs that came before them. A truly great DJ isn't merely a technical master and knowledgeable disc jockey, but an artist of sound and energy. Study the greats first, make note of how they were unique, and then take your inspirations with you as you practice your craft. The basics must always come first, but greatness comes when you develop a style that is uniquely your own.
Build up your knowledge of all musical styles. Keep an open mind even with styles that aren't your favorites. The more music you listen to, the easier time you'll have figuring out how to mix beats. After you've augmented your musical vocabulary, start small with the basic equipment. Acquire a couple turntables, a laptop with DJ software, and your favorite disco, dance, hip-hop and techno tracks. Before you get yourself booked at a club or party, spend plenty of time practicing your mixing. The more you practice, the more confidence you'll get.
Start spinning at clubs and parties. Start small, just to get a feel for the real stage. As you develop the complexity of your sets, try to go for bigger and bigger venues. Start where you live, DJing for friends at parties. Eventually take your improving skills to a bigger city like Chicago or Philadelphia, but plan on someday moving to LA or New York. Plan for growth. Always be on the lookout for new equipment, software updates and old records and new singles. A great DJ never stops expanding his capabilities. When he isn't entirely occupied on the party he's spinning for at the moment, he's thinking about how he'll be able to make the next party he works even hotter.