Prepare a glass of water at room temperature. Mix it with salt in the proportion of 1/4 tea spoons to one glass.

Take the salted water into your palm, close one nostril with your finger and inhale the water through the other nostril. Spit it out through the mouth. Do the same with another nostril. Alternating nostril use up all the water in the glass.

If you swim in the sea and immerse your head in the water, especially when there are waves, you have basically already done this practice.