Mantra WU is a very good mantra to bring the mind to a decent level of stillness in a relatively short period of time. I was amazed of its effects when I finally learned how to do it properly. I searched for years on how to actually do it, because it’s not fully clear from the description in Samael’s books. Finally I learned how to do it correctly.
After getting in a comfortable position, start relaxing your body. Once that’s done, move to vocalizing the mantra Wu. You have to imitate the sound of a hurricane, a strong wind, which is the sound similar to vowel U. However, you do not release the sound U in its full tone as it’s usually pronounced. Instead, you want to create it’s subtle aspect, centered in the throat. Like the sound of a hurricane. Experiment with this and see how it affects you. Once you reached the stillness of the mind, stop vocalizing the mantra. From there on you can move to another practice, or you can just continue sitting still with eyes closed, enjoying the inner peacefulness. What I like to do after this practice is observing my sense of self, my consciousness. Focusing on consciousness can enable you to go deeper within yourself and reach various insights.
You can also use mantra WU as the preparatory stage into practices that require great focus of the mind, such as astral projection, analysis of the subconscious state, etc. You can also just continue pronouncing the mantra for longer to see how much more can you silence the mind. Another thing you can do is to vocalize it only mentally, and trying to reach complete silence, in all the levels of the mind. Whatever you decide to do, don’t be afraid of experimenting with it.
Wu Wen chanted the mantra “WU”; with “U,” he imitated the sound of the wind in a mountain ravine and the sound of the sea crashing against the beach. Wu Wen knew how to intelligently combine meditation and sleep. Wu Wen vocalized his mantra mentally and thought of nothing. – from the book The Buddha’s Necklace by Samael Aun Weor