Om Mani Padme Hum is believed to invoke Avalokiteshvara, the protector from danger and the representation of compassion. The mantra can be recited by anyone who treads the path of love and compassion. Spinning a prayer wheel with this mantra inscribed is believed to be as beneficial as chanting the mantra.
While chanting the mantra, the focus should be on its meaning, which can be generally thought of as follows:
Om (or Aum), the cosmic sound, contains three letters - A, U and M - which symbolize the impure body, mind and speech of those who chant the mantra as well as the exalted body of Buddha, his mind and speech.
Mani is a representation of the intention of the practitioner to achieve superior levels of compassion and enlightenment. It is capable of fulfilling one's worldly and inner needs.
Padme symbolizes wisdom. Wisdom leads to realizing one's inner self by aiding in achieving perseverance, focus and perfection.
Hum helps to perfect the practice of wisdom.