I'm gonna go ahead and assume that you're using the 18-55 kit lens, which is probably a f/3.5 lens or someshit like that. That means that it's not going to let a ton of light pass through it. A f/1.8 lens, like the one you're going to buy, lets a whole shitload of light in, thus, you can shoot with a faster shutter speed and reduce motion blur.
What you need to do is google some subjects regarding esposure, aperture, and stuff like that
edit: just found out I'm gonna be going to NYC for the new year. FUCK YEA!
Gonna take a couple cameras, some rolls of film, and hope for the best. I'm expecting that it's gonna be pandemonium.