Ever listen to certain emcees, and wonder how they could spit endless multies, or how fast they spit? It's all about breath control. A start to getting better at keeping yourself from running out of breath, is to first get stronger lungs, in order to do this, you must first:
EXHALE: all of the air in your lungs and hold it for 5 seconds, be careful though because you can possibly collapse your lungs. (seriously) LOL.
THEN: INHALE: fill your lungs with air, and hold your breath for 5 seconds,do this 5 times a day, for stronger lungs. And I can guarantee you, better lungs in 2 weeks. Peace.