Pranayam

• To do Pranayam, sit relaxed in a well-ventilated place, preferably in a garden or near a tree. Sit on a chair or on the floor.

• Sit relaxed and try to calm down for a few minutes.

• Keep your body straight, backbone stiff, head up, chest out, eyes facing in
  front.

• Place the right thumb on the right nostril, and inhale  slowly through the left nostril. Keep inhaling slowly, until you feel at ease, as long as you conveniently can. While inhaling, let the mind not be vacant. Observe the very act of you inhaling. As days go by you will be able to witness yourself watching the breath and your thoughts.

• When you think you have inhaled to your best ability close the left nostril, through which you were inhaling, with two middle fingers. Thus when you closed both the nostrils, do not let the breath escape through the mouth; keep the inhaled breath within you in the lungs, in the stomach, in the abdomen; all the cavities being filled with air, the air which you have inhaled.

• When the breathed air is within you, let the mind not be vacant. Observe the very act of you holding the air.  As days go with this practice you will be able to witness yourself watching the breath and your thoughts. Your mind will wander but keep observing the thoughts.

• When you think that you cannot hold the breath any longer, then, keeping the left nostril closed, open the right nostril slowly, gradually exhale through the right nostril. Here let the mind not be vacant; let it observe the very act of exhaling.

• When you have exhaled, when you have breathed out as far as you  conveniently can, take off the hand from your nose; don't allow the air to come in for sometime, for as long as you can, and while, by your efforts the air is not allowed to enter the lungs through the nostrils, let the mind again observe the whole process.

• Then allow the breath to fill your nostrils. Inhale and exhale just as you would inhale and exhale rapidly after taking a long walk. This natural inhalation and exhalation which will go on very rapidly is Pranayam by itself. This is our
  natural Pranayam. After resting, by allowing your lungs to inhale and exhale for sometime, begin again.

Thus in this Pranayam, you went through four steps, both physical and mental:

The first step was inhaling. The inhaling part was the physical process, and observing was a mental process. 

Again, while you kept the breath in your lungs, there was a double process, the physical process of keeping it in your lungs, and the mental process of observing.

In the third step, you exhaled through the right nostril.

Then there was the fourth step of keeping the breath outside.

Thus the first half of Pranayam is done with this fourth step: One-half is finished.

• Now begin again, not with the left nostril but with the right one. Mental process is the same as before. Inhale through the right nostril, and while inhaling, observe the very act of inhaling.

• After inhaling to your fill, as long as you conveniently can, keep the breath within you and observe your thoughts.

• After that, exhale through the left nostril.

• Follow as you did with the left nostril.