You must be well rested before you start. The best time is after a good night's sleep, a light breakfast and a brisk walk. Lie down, head pointing north, feet pointing south, on a comfortable surface. Close your eyes and relax -- easy to say, but tough to do.
A number of techniques can be utilized to achieve a state of emotional, physical and mental relaxation. Eckhart Tolle suggests focusing on the contact of your body with the environment. Yoga teaches that the mind should be focused on your breathing. Another popular technique is relaxing your extremities one by one, starting with your foot and ending with your face. What these and similar techniques have in common is establishing a focal point to rein in your thought processes. Do not progress beyond this step until you can comfortably be here now without thinking.
At the completion of the initial step, you will be in what is known as a hypnagogic state, the twilight zone between consciousness and unconsciousness. While in this state of extreme relaxation, raise one arm and keep it raised. If you start to slip into sleep, the arm will start to fall and rouse you. Remain passive. If images and sounds come to mind, observe these mental phenomena, but do so without thought or judgment.
When mental noise has run down to silence, with your eyes still closed, focus on your visual input. You will probably notice lights and patterns on the inside of your eyelids. Ignore them. Continue looking at the inside of your eyelids until your field of vision is uniform. When this occurs, switch your attention from looking to feeling. Feel only physical pressure, not emotions. What you are feeling is what some call your "astral body." Pay attention to movement within the pressure. The movement is where your astral body is not totally locked into your physical body. Remain in your hypnagogic state, passively feeling the movement of your astral body within its physical shell. When the time is right, you will exteriorize.