From The Tibetan Buddhist Tradition
Tibetan Buddhist mantras are words originally spoken by a Buddha while deep in meditation. Reciting them helps to replace the endless, internal chatter of the mind with calming syllables that purify karmic imprints, bring beneficial energy, focus the concentration, and offer protection and blessings, according to this tradition.
The most commonly practiced mantra is OM MANIPADME HUM, the principal mantra of Avalokiteshvara, the bodhisattva who embodies the compassion of all buddhas. A bodhisattva is a compassionate Buddhist being who has reached enlightenment but delays entering paradise to help others.
The development of impartial love and compassion is the essence of spiritual practice; in the same way, this mantra is the essence of all mantras.
As you are reciting OM MANIPADME HUM, you can add the Hakini Hand mudra illustrated in this brief (1 minute 17 secs) video below. As a bonus, the Hakini mudra is thought to help balance the brain hemispheres, improve memory and increases clarity. Enjoy!