Breath is very important for our life and as well as for Yoga. No breath, no life, so In yoga we called it "Prana Shakti" means the "breath life force" or "vital energy". Normally in yoga classes beginners find difficulty to follow the flow of breath, they feel dizzy, headache or tired.The thing is in starting students wanna compare their breath with the teacher, but they can't follow properly so they feel these kinds of problems, also they are not aware of proper breathing pattern of yoga.
        In yoga breath should be deep, calm, peaceful and relax.In the beginning may students can't follow the proper Abdomenal breathing, so no need to worry, what you have to do is just deep inhale and feel the breath, watch your breath, fill up your lungs,diaphragm slightly raise up, just feel full of breath the Prana Shakti, and then slowly exhale in a very gentle way, if you can then try to stretch your exhalation double time than your inhalation. While inhale feel that you are taking in the vital energy, the shakti, positive energy inside of your body, and when exhale try to feel that the bad thoughts, negative energy taking outside from your body. So like this we can purify our breath, body, mind and soul. But remember no matter what, don't force yourself to breath in or out, try to enjoy the natural way of breathing. In the begginning may you feel hard, but don't worry, just try to deep inhale in a gentle way, and fill up your lungs, deep exhale and empty your lungs, try to feel your breath..

Enjoy the practice and watch your breath....

Namaste,
 Manu