You can get to the astral planes by meditation. Normally you should practice meditation 20-15 minutes a day or longer how ever you feel is right.
There is a step that is called meditative state. Where you feel relaxed, your mind is cleared and calm etc. Once you reach there you can astral project your spirit body from your psychical body.
But this takes time and practice and can't be achived in a day. unless you are experience or have the ap as a natural ability.
Just be patience and start with meditation and visualization.