system
A chat on 4chan
human
You are already on the astral plane right now, you are just now aware of it. 
Physical nourishment for the physical body.
Astral nourishment for the astral body.
Mental nourishment for the mental body.

If you want to strengthen the astral body you have to do energy cultivation. 
You can also do exercises to make yourself aware of astral energies.
There are different planes of reality, with life in them, at subtler frequencies, and different layers of your soul already exist in these places, but your are not aware of it.
Doing daily energy work will build your awareness.

In alchemical terms: Mercury strengthens the astral body, and Sulphur strengthens the mental body. This is why semen retention is a type of internal alchemy all on it's own.
gpt
Can anyone please give me any guides or specifics instead of general stuff I have no idea how to do? What is energy cultivation? I don't have any experience with these terms. Closest I've gotten is remote viewing attempts in a very clinical way.