its simple but time consuming and absolutely no harm would be done.
also you need to attend a ten day vipassana camp of sn goenka.
The 4 Jhana
you just have to go to a stage which is called sxth jhana. some information and steps on how to achieve it: About Potthapada.
While rupajhanas differ considering their characteristics, arupajhanas differ as their object is determined by the level of the jhana:
fifth jhana: infinite space, sixth jhana: infinite consciousness, seventh jhana: infinite nothingness, eighth jhana: neither perception nor non-perception. This has to be understood. In the fourth rupajhana, there is already Upekkha, equanimity and Ekkagata, concentration, but the mind is still focused on a “material” object, as any color.
In the fifth jhana, the meditator discovers that there is no object, but only an infinite space, which is empty. This perception motivates the interest of claiming arupajhanas. In the sixth jhana, it becomes obvious that space has no existence. There is only infinite consciousness. In the seventh jhana appears the feeling that there is no consciousness, but nothingness. The eighth jhana consists in the most discrete possible state of mind, which justifies the using of “neither perception nor non-perception”.
This answer originally appeared on this Quora question on Astral Projection.