In the last 15 years-ish I've ready every book on astral projection and out of body experiences I could get my hands on. I've always felt that new books must have something new to say, some new technique or insight I might be missing.
We're being flooded with offers for gadgets and pills telling us it's the answer to astral projection. Yet if any of that crap actually worked it'd be a big news story.
Journeys Out of the Body is one of the original books on astral projection. Some don't like it because they think it's outdated based on the cover but this stuff has not changed. The new 'techniques' people tout are just shit to get views on YouTube or sell some magic astral projection pill.
The book might be old - but it's the only one which reads like a lab report. Every astral traveller I've met has read it at least once. It's sold over 300,000 copies for a reason - and it continues to sell to this day.
I won't tell you this is the only way to learn to astral project. But I will tell you I've read a lot of these books and this is the one which made a real difference to me.
The fact that Amazon give you the audio-book here is a bonus. You can listen to it while in the car or just falling asleep. Personally I like to listen to it a couple of times over to make sure I've really got everything from the book. Sure, you can read it as well but I always feel like I'm being the most productive when I can listen to self improvement stuff while I'd otherwise be wasting time.