The wai is the common form of greeting and adheres to strict rules of protocol.
Raising both hands, palms joined with the fingers pointing upwards as if in prayer, lightly touching the body somewhere between the chest and the forehead, is the standard form.
The wai is both a sign of respect as well as a greeting. Respect and courtesy are demonstrated by the height at which the hands are held and how low the head comes down to meet the thumbs of both hands.