Sitting on a chair with your spine straight, visualize a rope descending from the tail of your spine. See it go through the floor, down through the earth, then the layers of rock, until you feel that you are near the center of the earth, then anchor the rope there. You can also visualize your body going through the earth with the rope and, having anchored it, come back to your sitting position.
Now imagine that there are two holes in the bottom of your feet and that a heavy brownish-red warm sludge is coming up through these holes and circulating throughout your lower body. Do this until your lower body feels heavier. Then visualize a distant point in the heavens from which a beam of white light is coming down to connect with a point on the crown of your head. Feel the white light flow through this point into your head and through the upper part of your body, cleansing it and making it feel lighter.
Now feel the two different energies circulating at the same time and finish the exercise by touching the floor with your hands to allow any excess energy to return to the earth. This exercise takes only a few minutes to do.
As with all visualization exercises, don't become obsessed with trying to see everything clearly - forming the idea in your mind is enough to make it work.
~From: Healing Reiki