From Wikipedia: Drawing down the Moon (also known as drawing down the Goddess) is a central ritual in many contemporary Wiccan traditions. During the ritual, a coven's High Priestess enters a trance and requests that the Goddess or Triple Goddess, symbolized by the Moon, enter her body and speak through her. The High Priestess may be aided by the High Priest, who invokes the spirit of the Goddess. During her trance, the High Priestess speaks and acts as the Goddess.
I personally have no stylized ritual for drawing down the moon. I go outside during the full moon and ground myself. Once I've grounded, I raise my hands to the moon and ask fro Her power to come down into me. Sometimes it happens right away, sometimes it take a while.
Here is a great ritual for those who follow Hekate, like me! In fact, that whole website is great for information on Hekate!