During my teens and early twenties I had quite a few OOBE's without any external assistance, these days I'm too tired generally and don't have the mental energy nor the drive for it anymore - they were interesting experiences but, like DMT, didn't give me what I was really (still) looking for.
You need to be fresh, no sleep debt or fatigue, otherwise it is just too easy to slip into sleep. I always found that the best time was before lunch (digestion takes blood and energy, more liable to sleep).. you're sharp, breakfast is digested.
Lay down, or better if you own a recliner chair! Regular deep breathing for a minute to calm the body and mind, then relax the breathing, and pay close attention to the body as if you were like a hand inside a glove. Don't pay any particular interest to thoughts but don't let your mind wander into fantasy or recede into sleep, stay focused but relaxed. Your body will eventually start to feel heavy, then feel like your attention is receding inwards.. my 'head' always used to feel massive, sounds got muted but expansive like I was inside an empty silent football stadium..
This is now the crossover point and it's easy to slip into sleep and twirl off into a fantasy. Just stay self-aware, the body will fall asleep, and then exert will to move the body (can't, it's asleep).. the mind will then project outwards.
Never really got that far, my attention always waned after about 10 seconds. I would see my room and take in the sensation of it all.. then my attention would slip and it would turn from a projection into a dream.
Once I became convinced of the validity of the mind existing separately from the body I kind of lost interest in it. I mean what is difference between exploring there or exploring the physical world?