To enjoy smooth respiration, you need to take care that both the nostrils should be clear and the passage within them should be completely open for air to move. But with many people, it is usually only one of the nostrils that is open. Hence it is important for you to clean the nasal passage. Yoga gives a kriya called Neti which is useful for clearing the nostrils.
In Neti, a thick thread of about one foot made by interlacing three or four thin threads and softened with butter or oil is passed through one of the nostrils and is brought out through the mouth. Hold both the ends of the thread together and rub the nasal passage by pulling both the ends of the thread, alternating to and fro. When you finish cleaning one nostril, take out the thread from the mouth. Wash the thread properly and insert it in the other nostril. Repeat the process. You can replace the thread with a rubber catheter and derive the same purpose.
You can also perform a milder version of Neti by pouring lukewarm water with a dash of table salt through a cup with a spout into your nostril. You stoop slightly forward and tilt your head to a side to pour water. Do not permit the water to go down the throat but it should come out through the other nostril.
Drinking water through the nose can be another form of Neti. The water should not be either too cold or too warm. Take this water in a bowl, dip your nostrils slightly into the bowl and then tilt it. Suck the water gently and let it go down the nostrils. This will irritate the inside of the nasal passage initially, since the upper side of the nasal passage is very delicate and water will irritate it. But regular practice will teach you to pass the water through the lower nostril, so there is no irritation. This method is very useful in warm climates as it cleans the nasal passage and has a soothing and refreshing effect on the nasal canal, brain and eyes.
As per tradition, water is kept in a copper vessel overnight and is drunk through the nose early in the morning. Once you get the experience, you can easily empty an entire glass of water within a minute or two. You can then enjoy the yogic breathing after cleaning both the nostrils. But people with a deviated nasal septum or any breathing disorder should always take medical advice before doing yogic breathing.