According to Crystalinks.com, astral projection occurs when the conscious mind leaves the physical body and enters the astral body. The conscious mind is aware of things encountered while out of the physical body. One must be reclining, relaxed and in comfortable clothes to astral project, and a comforter is recommended, as the physical body may cool with the absence of the conscious mind.
There are two schools of thought in astral projection. The Phase Model holds that it is impossible to leave the physical body, but the projector actually phases into another level of consciousness, like tuning the radio to another station. In this model, there are different locales to visit based on the level of consciousness.
The Mystic Model encompasses myriad belief systems and maps of the astral world, but holds the common belief that astral projection takes place outside the body. Believers of this model hold that a subtle energy body carries the consciousness, and that it is attached to the physical body through an energetic connection, usually in the form of a silver umbilical cord.
Jerry Gross, an expert in out-of-body experiences, states that everyone is born with the ability to astral project. Gross posits that astral projection is inherent during childhood, and it can be developed like a muscle, but the ability may be lost through neglect.