When the basic pattern of nadi shodhana is comfortable, the student can change the ratios of inhalations to exhalations. Initially the ratios are 1:1 – four count inhale: four count exhale or 1:2 – four count inhale: eight count exhale. When antar kumbhaka is added, the ratio can be 1:1:1, or 1:1:2. If the bahir kumbhaka is also added the counts can be 1:1:1:1 or 1:1:2:1. Once these ratios have been practiced and are comfortable, the ratio can be increased to 1:2:2:1, and then to 1:2:4:1. As always, this should never be forced. According to the Yoga Sutra, the breath needs to be even or calm (sukshma), while being long (dirgha).
Breathing in through the left nostril engages the energy along the ida nadi, which is the lunar or yin channel; breathing out relaxes that energy. Breathing in through the right nostril engages the energy along the pingala nadi, which is the solar or yang channel; breathing out relaxes that energy. Alternating the breath, through both channels, brings balance to the nervous system, and the mind becomes calm and still.
If one nostril is plugged, that nostril need not be completely closed. Generally you will find one nostril is more open than the other. This is normal, and nadi shodhana will even the flow in both sides. If both nostrils are closed, perhaps due to a cold or some other nasal infection or condition, pranayama should be avoided until the illness has passed.
Neti, another of the six cleanses listed in the Hatha Yoga Pradipika, can be used to clean the nose and facilitate nadi shodhana. In neti, warm distilled or filtered (non-chlorinated) water, with some sea salt added,  is poured into one nostril and drained out through the other nostril, or through the mouth. Other liquids can be used, such as milk or even warm ghee.  The professional yogis use a string threaded through one nostril and the mouth, gently pulling the thread back and forth, cleaning the nasal passage. Needless to say, these practices are not for the weak of stomach, and should be learned from a teacher.
Nadi shodhana can also be used to open one side of the body. If a day has been quite yang-like, you may want to just breathe in and out through the yin channel. Close the right nostril, and breathe in and out through the left nostril; add the retentions if desired. The yin energy will be stimulated and will balance the yang energies.
On the other hand you may have had a day that is too yin-like, and you need to add some yang energy. In this case, close the left nostril and keep it closed, as you breathe in and out through the right side. This can also be done just after a yin practice, if you still feel you are in an altered state; engage your yang energies by closing the left nostril, and breathe for a while through the right side only.
Another way to manipulate and manage our energies, beyond vinyasa and pranayama, is by meditation. We will examine this practice next.