Empty the brain. Do this before going to bed. Every night , I sit in Baddha Konasana and I use kettle bells to help push the knees down. At the same time, I do a ten breath exercise, 15 second inhale, 15 second hold, and a 20 second exhale.
Sometime I will do a mantra with a Mala. A Mala is a neck less with 108 beads. The Mala I have is made of wood from a boddhi tree and was blessed. I believe the mala was an inspiration for the Christian Rosary, just like prayer hands, Amen, the trinity, and the rosary may have it’s origin in Indian culture. A mantra could be anything or something from antiquity. The words are said 108 times with the word Om said afterwards.
A sacred mantra is the Gayati Mantra which was in a recent posting on Facebook, sanskriti. Here is the link. http://www.sanskritimagazine.com/indian-religions/hinduism/gayatri-mantra/ust I believe one should be trying to follow the Yamas and Niyamas before reciting this mantra. I would repent any sins before doing this. Below is a YouTube link to the Gayatri Mantra:
The Yoga Bridge 