What are the steps to perform breathing meditation?

The simplest, most elegant and accessible breathing meditation technique is called "Sohum Sadhana". The way to perform it is the following:
1. Sit in a comfortable posture. Any posture which you can maintain without unsure stress anywhere on the body is fine.
2. Close your eyes.
3. Breathe in and out as you normally would.
4. While inhaling, mentally recite the syllable "So", with a long "o", which stretches as long as inhalation action continues.
5. While exhaling, mentally recite the syllable "hum", with the "um" pronounced as in "rum". Let the ending "m" sound continue until the end of the exhalation action.
6. Keeps repeating steps 5 and 6 as long as you want.