My words are in italic – the rest is from Yogi Bhajan. (the significant information in bold):
Meditation for focus and mental purification
Here is a meditation that makes use of prana to cleanse mental garbage and purify the mind. Of all the 20 types of yoga, including Kundalini yoga, this is the highest kriya. This is a very powerful meditation for prosperity. It will give you a new start. It is the simplest kriya, but at the same time the hardest. It cuts through all darkness and all barriers of the neurotic or psychotic nature. When a person is in a very bad state, techniques imposed form the outside will not work. The pressure has to be stimulated from within.
The tragedy of life is when the subconscious releases garbage into the conscious mind. This kriya invokes the Kundalini to give you the necessary vitality and intuition to combat the negative effects of the subconscious mind.
POSITION: Sit with a straight spine (either with legs crossed or sitting on a chair with feet flat on the ground) Eyes are focused at the tip of the nose, or closed if you prefer.
MUDRA AND BREATH:
a) Block off the right nostril with the right thumb. Inhale slowly and deeply through the left nostril and hold the breath.
Mentally chant ‘Wahe Guru” 16 times, while pumping the navel point 3 times with each repetition (once on ”Waa”, once on ”hey”, and once on ”Guru”) for a total of 48 pumps.
b) Unblock the right nostril and use the right index or pinkie finger to block the left nostril. Exhale slowly and deeply through the right nostril. Continue, inhaling left nostril, exhaling right.
TO END: Inhale and hold 5-10 seconds. Exhale. Then stretch and shake the body for about 1 minute to circulate the energy.
TIME: Suggested length for this kriya is 31 or 62 minutes a day. The ideal is to start at 31 minutes, but you can begin with 11 minutes, then build up to 31, then 40, and eventually 62.
* There is no time, no place, no space, and no condition attached to this meditation.
Each garbage pit has its own time to clear. If you are going to clean your own garbage, you must estimate and clean it as fast as you can, or as slow as you want. You have to decide how much time you have to dean up your garbage pit.
COMMENTS: If you can do this meditation for 62 minutes to start with, then build up to the point where you can do it 2 1/2 hours a day (1/10 of the day), it will give you the following: ”Nao nidhi, athara sidhi,” which are the nine precious virtues and 18 occult powers. In these 27 total virtues of the world lies the entire universe.
When practiced for 2 1/2 hours every day, it will make you a perfect superhuman. It purifies the subconscious and takes care of the human life. It will make you extremely intuitive. It brings together all 27 facets of life and makes a human saintly, successful, and qualified. This meditation also gives one pranic power. This kriya never fails. It can give one inner happiness, and bring one to a state of ecstasy in life.
(as taught by Yogi Bhajan on December 1990)
This basic instruction is what I worked with on my own for 24 years and I still follow it.
here is more information