Listen to lots of rap. If you want to rap, you've got to immerse yourself in the culture and the sounds of hip-hop and rap music. It's a style of music deeply ingrained in city life and culture. Find an artist you like and trace their influences back to get some sense of the foundation of hip-hop and develop your knowledge of the style. Listen to popular rap artists, listen to underground artists, listen to old-school rappers, listen to Nas.