Mark's books were decent for that time though with some abstractions.
There's the
cheat way to do it by exploiting the mind's intelligence via
yoga nidra like Utopian is saying and then there's the
surefire way by developing the specific siddhi.
The books authored and online offer various and creative cheat ways and some work better than others, Bob Monroe is among my favorite as well as some things Sylvan Muldoon and Heward Carrington were doing. Robert Bruce has offered a somewhat comprehensive course in the process as well.
What most people end up doing is having lucid dreams that they are flying around outside the body so as you probably know this gets tricky.
You won't find any material on the siddhi process because it is given as pith from Master to student after attainment the enlightened state. The path towards the enlightened state involves cleaning and correcting to allow divine influence into your energy meridians and the siddhis can develop during this process.
One can consider the intention first, why are we doing it?
