The natural place of our astral body is either with our physical body or with our Higher Self - our quantum interface to the Universe.
At some stages of our sleep, the astral body leaves our physical body to join Higher Self briefly. This is one of the fundamental functions of sleep.
For this reason the easiest way to experience astral body freedom is to learn to become conscious and fully aware during sleep when the opportunity arises.
Two skills: meditation and concentration are needed to attain, sustain and enjoy the experience.
You need to learn to meditate and concentrate reliably and very well during your daily life before you attempt to wake up in the astral body.
Also, you need to have a good reason to experience freedom from the physical body. If your reason is not good enough for you and/or for the Universe - your Higher Self can restrict or prevent your astral experiences.