Analog Vilom

There is a whole branch of  Yoga solely dedicated to breathing exercises. This branch of yoga is called pranayama. 

While there are many different kinds of yoga practice dedicated to breathing, perhaps the most common of Prayanama exercises is Anulom Vilom. Sometimes it is referred to as alternate nostril breathing. To do it, you simply use your finger to restrict your breathing in one nostril and then breathe in and out with the non-restricted nostril.