To get real knowledge you must experience, and not read or believe the words of others. Thus, the best to do is read something practical, that you can turn into a way to explore what you are told to find the truth on your own.

This would then mean that the most beneficial of anything you can ever read, and practice, would be topics on Astral Projection, Lucid Dreaming, Psychology and Consciousness.

As far as more philosophical material, any older texts on gonsticism, hermetics, kabbalistics, buddhism, egytpian etc can be rewarding.

When you come to understand true alchemy you are on the way.