Sit at a table with your face toward the east, rest your elbows on the table and proceed in the following way:
Insert the thumbs of your right and left hands into the ears. Cover your eyes with your index fingers, cover your nostrils with your middle fingers, and seal your lips with your ring and little fingers. Breathe in slowly counting from one to twenty. Hold your breath and count from one to twenty. Exhale slowly counting from one to twenty. It is necessary to remove the middle fingers from the nostrils to inhale and exhale, but during the retention of the breath the middle fingers should seal the nostrils.
It is necessary that during the retention of breath to try to see the tattvas with the third eye –the third eye resides between the two eyebrows–. At first you will not see anything, but after some time you will be able to see them and recognize them by their colors. Akasha is black and its planet is Saturn. Vayu is blue-green and its planet is Mercury. Tejas is red like fire and its planet Mars. Prithvi is golden yellow and its planet is the Sun –also influenced by Jupiter–. Apas is white and its planets are Venus and the Moon.
Samael Aun Weor
Introduction to Gnosis, chapter 3