astral projection - generally

Astral projection (or astral travel) is an interpretation of any form of out-of-body experience (OBE) that assumes the existence of an "astral body" separate from the physical body and capable of travelling outside it. Astral projection or travel denotes the astral body leaving the physical body to travel in the astral plane.
The idea of astral travel is rooted in common worldwide religious accounts of the afterlife in which the consciousness' or soul's journey or "ascent" is described in such terms as "an...out-of body experience, wherein the spiritual traveller leaves the physical body and travels in his/her subtle body (or dreambody or astral body) into ‘higher’ realms." It is therefore associated with near death experiences and is also frequently reported as spontaneously experienced in association with sleep and dreams, illness, surgical operations, drug experiences, sleep paralysis and forms of meditation.
It is also sometimes attempted for its own sake, or may be believed to be necessary to, or the result of, some forms of spiritual practice.

The following text is copied from http://www.astralvoyage.com, and it's written by the guy who made the site:

First, what is astral projection? Astral projection is simply the transferring of the consciousness from the physical body to the astral body. We have several 'vehicles' for our consciousness, and the astral body is one of them.

Now, I will outline the progress of how I learned to astral project:



Desire:
First is the desire. I have a friend who experiences the beginning states of astral projection, but has no interest in pursuing it, therefore never goes anywhere. "Why?" she asks. Well, if you don't build the interest and suitable desire, you're more than likely to go nowhere, and that is probably as it should be. We are all on individual paths, and no one can judge the course of another.

Fear:
"Fear is the great barrier to human growth." Robert Monroe, Ultimate Journey. This is why once you've built the desire, relaxed and can concentrate, you need to lose the fear. One of the biggest obstacles is the initial fear of the vibrational stage. There is also the fear that you'll die; fear that you won't come back; fear that your body will be possessed. I have never known of anyone to suffer any of these ailments. In fact, after visiting a particularly gorgeous place, I'll do everything in my power to NOT come back! But to no avail! No matter what you do, you WILL come back (unless of course you have a heart attack in the middle of your sleep). Fear is a reoccurring theme (and/or lesson) that people have to overcome in order to advance in astral projection. You're not alone; everyone, at some time or another, will have to surpass one of the biggest obstacles. This theme, however, applies to all areas of our life, so when you can overcome this one, your whole life will be enriched. I've read a vast array of books, talked with many people on this subject, and I have drawn one conclusion, and that is to face it. You can read until you're blue in the face on how to deal with fear, how to control your emotions, that there's nothing to fear but fear itself, but until you face it head on and overcome it, these will be just words. And even when you face it and think you have learned the lesson, it will take on another shape and another form and reoccur until the lesson is thoroughly worked out. Then you will see it disappear from your life because it is no longer needed. I met my guide once in the astral and he told me that there were seven cycles of life and fear is one of them. We will cycle through these lessons until each one is resolved. What happens in our life is neutral, and it's up to us to view it as positive, negative, spiritual, or mundane.

Concentration:
One of my personal big obstacles! I can relax just fine, but when I try and quiet my mind and focus on one thing, a thought slips in and I'm off on a fantasy. My most successful attempts are when I can clear the mind and use several techniques; either focusing on my third eye, using a particular visualization tool or affirmation. Practice concentration, via meditation, looking at candles, or whatever your preference is. Robert Peterson in "Out of Body Experiences" states that, "The single most important factor in leaving the body is that you focus your consciousness down to a single, focused, barely noticeable thread." Do you ever stop and listen for that "high pitched noise" in your head? Sometimes, if it's really quiet, I can stop and listen for it. Robert Peterson states that if you can hold your concentration on this very noise for three minutes that the vibrations will rush in.

Relaxation:
Countless people have repeatedly stressed this and that's because it's true. If you're upset over a job, spouse, health, finances, or whatever, more than likely this will be what is consuming you, not astral projection. Clear your load if you want to pursue astral projection. We cannot escape work, loved ones, bills or traffic, but we can do a little to minimize the "noise" in our life and this may also include having to make long term decisions. Is your career keeping you from pursuing the higher things? Are you accumulating too much physical goodies via credit which perpetuates the stressful job in order to pay for them and thus keeps you up at night? Is your spouse in tune with you and your goals, or creating disharmony? If we want to project, we eventually have to lead a lifestyle that is conducive to it. We cannot live like monks in a quiet monastery, but we do have choices and we can chose compatible mates, get less stressful jobs, work towards simple lifestyles that allow for freedom and more quiet time.

And this is what they say about it on http://www.crystalinks.com/astral.html

Reality is created by thought projection (consciousness) into the physical. There are 5 subtle bodies In astral projection the conscious mind leaves the physical body and moves into the astral body to experience. In astral projection you remain attached to your physical body by a 'silver umbilical type cord'. Some people are able to see the cord when astral projecting. To astral project, as with all out-of-body experiences, one must feel totally relaxed, clothing fitting comfortable, reclining is best. Often a comforter is best over the body as the physical body sometimes gets cold when you travel out.

When you astral project you are consciously aware of things you encounter while out of your physical body.

Some people can astral project naturally. Others are afraid to remove their consciousness from the physical body and never learn to astral project.

Astral projection (or astral travel) is an out-of-body experience achieved either awake or via lucid dreaming or deep meditation. People who say they experience astral projection often say that their spirit or astral body has left their physical body and moves in another dimension known as the spirit world or astral plane. The concept of astral projection has been around and practiced for thousands of years, dating back to ancient China. It is currently often associated with the New Age movement.

So, that's about all.. I could write it myself, without copying, but this way I am sure this are real informations and not only based on few expiriences of mine.
You can visit those links for more information.