Astral projection is not always necessarily an out-of-body experience. It is a method of visualization, employing a deep meditative state.
While some people do achieve an out-of-body, fully immersive type of experience with relative ease, these cases are relatively rare.
The most successful method(s) of experiencing the astral are through guided or deliberate meditations of moving through an environment, into a means for transport to a different environment. For example, a person may visualize walking through a peaceful forest, to a lake below a cliff, then through a waterfall on the other side -- or even imagine ascending the waterfall. At a point, ideas or characters may present themselves at the top of the waterfall.
The astral is different for everyone. Since the images are all filtered through the practitioner's own mind, imagery will be specific to its meanings for that person. If someone wants to visit the same 'location,' they may have a very unique experience compared to someone else, though there might be correlation of some concepts and elements.
It is important to know that during astral projection, the spirit does not leave the body, regardless of what may be experienced. A person's awareness is basically extended to the Astral, as opposed to the material or mental. It is still important to use protection, wards, and the like, as defense is a good idea when paying strict attention to something else.