You may have heard of a triple threat—a person who has the three main performance talents necessary to take the stage. In the musical theater world, the more of these three talents you have, the better your chances are of actually making a career out of it.
Singing: you can carry a tune, can support a tune, and can harmonize with a cast of dozens of people. Perfect pitch wouldn't hurt, and the closer you can go to the extreme highs or lows, the better your odds of getting to sing all alone.
Acting: you can breathe life into your lines as well as any off-Broadway "legitimate" actor. Wooden delivery won't cut it, especially if the musical has speaking parts.
Dancing: you're physically fit and capable of interesting and/or entertaining body movements—and you have rhythm. You can move from ballroom to tap to hip-hop, sometimes all in the same song.
Are you skilled at all of these things? Great, so are thousands of other aspiring New Yorkers. The only way to rise above the noise is to make sure you're always practicing and rehearsing those skills. What gives you a fighting chance in musical theater is guts, grit, and ambition—and a heavy dose of actual talent.