Visama Vritti Pranayama

In the Visama Vritti Pranamayama practice, the breath is controlled in order to make the exhalation exactly twice the length of the inhalation.
This is a more challenging practice than Sama Vritti Pranayama, which should be practiced first.

Technique
Sit quietly and comfortably with your eyes closed and start by just watching your breath for a few minutes. Start counting inwardly and notice the length of inhalation and exhalation. Which one is longer? Or maybe inhalation and exhalation are exactly the same length?
When you are ready to start, slow down the flow of the exhalation to make it twice as long as the inhalation. This requires fine control of the flow of the outbreath, so don't worry if you don't get it right the first time! In the first stage of the practice, keep the inhalation flowing naturally, only the exhalation is controlled.
Once this first stage of the practice is easy and comfortable, you can move to the second stage of the practice, in which you lengthen both inhalation and exhalation while keeping the exhalation exactly twice the length of the inhalation. Inward counting would be something like this: inhale 1-2-3-4 exhale 1-2-3-4-5-6-7-8. Proceed slowly and gradually so that you do not overstretch the breath, which must always remain smooth and comfortable. Practice for ten minutes every day until you can comfortably double the length of your natural inhalation. You can then move on to Nadi Shodhana.