Most choreographers will tell you how important mastering the art of breathing is to your ballet practice. Your first point of action is to understand how your body functions when it breathes in and out. Place one hand on your chest and one on your stomach. Breathe in and out a few times. If you notice that, as one goes up the other goes down, your breathing isn't coming in full from the belly of your lungs. Now focus on breathing; picture your lungs filling with air as you breathe in and out. If done properly, you notice now that your hands move at the same time. This control is what you need to practice, to remind you how to breathe.
Once you master the understanding of how to control your breathing, you must understand how breathing helps you to get more strength and longevity for your routines. If you tire easily, even at the beginning of your practice, it is likely you are not breathing properly. It's common to sometimes forget to breathe while you're in the middle of dancing or working out. While you focus on performing the activity, you may forget to inhale and exhale. Breathing gets the oxygen flowing, gives your muscles some energy, and helps you to push harder and commit to your poses and stretches.
Maintain proper posture while at the bar, or in the middle of your choreography. Give your lungs a full chance to take in and release the air it needs. Avoid slumping over or leaning forward too far. Keep your posture throughout your entire workout to maximize your success at growing into your routine quickly.
Work out often. Get in a proper cardio workout consistently to help you build your endurance. The workout also trains you for strengthening your core, balancing, and getting a good all-around aerobic exercise. Routine cardio work reveals how less winded you are after a few short weeks, as your body adjusts to the increased energy and exertion.