I started being able to effectively trigger lucid dreaming when I realized that there were some cues my mind and body would let on before going into a sleep session that resulted in lucid dreaming/astral experiences. Mind you, this is only what I've experienced and probably not the same for everyone. And this kind of stuff is sometimes hard to explain.
The first big cue I noticed was that a bit after laying down, I would feel this particular heaviness+wavy feeling between the top of my head and forehead (presumably third eye activity). If I caught it at the right time, I could almost flex that part of my brain it felt like, and start breathing as slow and deep as I could. Every breath I would try to sink into my body more. It would lead to a very particular feeling in the body. Slightly electrical. It's like that feeling you get in your body when you're dead tired, lay down and close your eyes and you feel your body drift, but you feel it while your mind is way more awake. Then you get to this point where you feel something very different, like a floating sensation. It's when you're awake + asleep.
Once I started listening to my body and mind more, and remember the different phases I would go through, my success rate shot up. And things like whenever I fasted, and even things you intake like
@Saturday mentioned.
I will say in all honesty though that it's been a while since I've really dedicated myself to it. Partly because I consume cannabis for medical reasons every night, which pretty much nulls out most dreams I'm supposed to be experiencing. It sort of sucks because right now in particular, I've taken on a new set of practices that require my dream state to be as vivid as possible so I can catch spirit communication. So this is something I need to actively start practicing again reducing my intake.
But keep at it! Every night! Keep a log next your bed with a pen in between the page you're going to be writing on. Dreams like to fade within seconds of awakening. Even if you don't lucid dream/astral travel/or dream at all that night, still write something down. Write down what you did differently the night before if anything. Maybe if you remember the last thing you were thinking about. The exercise becomes that over time you become more aware of your dream states and have a log you can refer back to of things that helped out or didn't help.
I've seen/heard the idea that your soul leaving your body can cause you to die tossed around a bit. I think in the most technical sense yes, if your soul leaves your body, you're effectively dead. But I think your astral body is different than your soul, more like the highest layer encapsulating your soul. To me, astral body/spirit are sort of synonymous.
I think of it like the our astral body/spirit being a drone, while the soul is the FPV pilot. The drone has a "tether" to it if you will, which determines the range and signal quality between drone to pilot. It seems like the there may be cosmic systems in place that provide that same kind of "tether" but with more restrictions. Like if you get too far, the astral drone returns to home automatically. Don't think there's ever been a recorded case of someone going into a coma or anything during meditation or attempted astral travel, although I may be wrong. And when you die, I think the pilot just gets communication cut with the old drone entirely and get connected to a different one.
All I'm trying to get to is that I'm pretty confident you can't astral travel too far, or anything of that matter. I've always been woken up before even feeling like that was a possibility. You could though, encounter some nasties out there which is a whole separate topic.