You need a journal. You need deliberate practice. You need progressive goals.
I did about 5 minutes every 2 to 10 days.
First, no other thoughts. I did mindful boxed breathing for about 3-4 minutes.
Then, a point. Something that is in a spot.
Then two points. Something like a distance.
When you have that, advance to a triangle. Then colored triangle.
Then a pyramid that you spin around, coloring different faces in different colors.
That alone took about 6 months of practice. Then it gets easier.
And then I had what was the most frightening thought I've ever had: "I don't know how to make this thing go away - what if I can't make it go away? Have I just taught and meditated myself into psychosis? Oh shit!!!"
I then pulled out of the visualization (no idea how that happened, it just ended with no fanfare, presumably as I started to think about other things) and have never seen another mental image like that, even though I've tried. This happened perhaps ten years ago.
That experience was not entirely unlike my experience with lucid dreaming some years earlier. I essentially never dreamed (never recalled my dreams), but I read all about lucid dreaming, thought about it, and used Richard Feynman's dream study approach to try to focus on it. Then one night I had a lucid dream, and the next night, and the next. Each night for almost a week I had an incredibly vivid lucid dream, absolutely amazing experiences, waking up the next morning with full recall of it and feeling exhausted and entirely unrefreshed from my sleep. At the end of that week I had a final dream. In that final dream the subject of my dream was the realization that I couldn't lucid dream any more. I never had another lucid dream, and have almost never remembered any dreams since then.
The hardware is clearly there for this stuff, at least in my case, but it seems the OS is also clearly working to "protect" me from some of those hardware features.
Given that there absolutely are people who are subject to uncontrolled hallucinations and mental breakdowns between the real and the imaginary, I've concluded that at least for my mind these experiences are too close to the boundary for whatever circuitry protects me from that sort of breakdown. Others will have their own journeys, but for me based on my personal experiences I've concluded it's not a case of the mind "can't" it's a case of the mind "shouldn't" or "wont."
As with any extreme training, be careful not to injure yourself. You might be fine, but not everyone who engages in extreme training does so without injury. I'm glad to have walked away from the process safely and can easily imagine not having done so.
Be more bold.
I was like you, very ambitious. Started with a cube, after many attempts getting nothing saw something incredibly vivid, very much like lucid dreams that I've had when I was younger.
And then three months of nothing again.
I got SO EXCITED. It's there! I was right, people condition themselves largely, into a form of acceptable experience. But there is more.
So I took smaller steps. A point. A spot of magnitude. Add color. Add one more spot, at a measure from the first. Rotate that around, then rotate that in three dimensions. Trace letters, one by one. Read backwards the result. Light a surface, texture a surface, bend a surface.
The smaller the steps the more success you'll have. It's important to feel grounded, and it's important to be motivated to invest the time. Success is non-negotiable, it has to be there.
Frustration is the mind killer.
