The title is far from perfect but the real core of this thread just won't fit into one line. I've learned from past attempts of making overly detailed threads though, so bear with me while I make this as short and concise as I can, so no one gets lost along the way.
Premise:
Think about when you learned how to use your body, like your hands, or holding breath, thinking simple things like 1+1=2 and other comparatively simple things you could still learn or have learned, like playing a certain game, swimming...
Now imagine being in your brain, setting behind an unfathomably huge panel of buttons, sliders and all kinds of other input devices. A normal life during a normal human life span is hardly going to scratch the surface of what this panel can do and there are some simple reasons for that.
1. Humans didn't need to in order to survive
2. Most of the really fancy things you can do hardly provide tangible input while attempting to learn how to do them

And the second point is what this thread is all about. We'll get there in a moment.

Now, imagine you completely forgot how to use one of your hands, or maybe one of your feet, how to move one of your eyes... you get it, whatever your current body allows you to imagine. If you attempt to relearn how to use that body part you'll be examining and randomly using your inner control panel until you find some of the right buttons and sliders and the body part you forgot how to control moves or twitches in some way. You got some tangible input that you can use while further examining the control panel and learning how to use which kind of input, when and how. For example you can think of the muscles in your body as countless sliders between relaxed and contracted, and addressing each of them makes your body move immediately so learning how to use them is relatively easy, and you're predisposed to having a easy time learning how to control them, because if you wouldn't be, you'd probably be dead.

Now for something possible, but MUCH more complicated. Imagine you want to learn how to see something that is not there. You're looking at a white wall and want to imagine a black shape on top of it and you want to clearly see it, eyes wide open. How would you do that? As a human you're not predisposed in the slightest to do something like that. There's a lot of exercises other people have invented that you could try, like starting with closed eyes, trying to change the phosphene's you see. Chances are you're going to have an excessively hard time even when you have a few ideas of where to start and what to try, because you're not just working with a simple slider as with muscles that provides an immediate feedback, but rather you need to address a whole sector of your control panel correctly at once before you're even going to begin seeing some results.
So, during the initial phase of learning how to do that you'll suffer from a gap between your input and the results.

And this is the question of this thread:
How can you imagine dealing with this gap in order to learn things that are far from natural? Like seeing/hearing/smelling/tasting/feeling things that aren't present outside of your own mind, turning your sensory pain input on/off at will, as a male turning your refractory period off, falling asleep at will...
I'm searching for general answers, not specific techniques for specific things.



And now for some additional info, if you only care for the core of this thread and have an answer to drop, skip the rest.



My own answer:
My most relevant answer is LSD. But because humans are outrageously stupid on a level that makes me wonder why some people's heads don't just spontaneously implode from the vacuum inside, LSD is illegal pretty much anywhere. Despite thousands of hard facts that clearly point out that the dangers of using LSD are incomparable to cigarettes and alcohol, and I don't mean LSD being the dangerous thing here. Also LSD has a lot of potentially beneficial medical applications whereas alcohol and cigarettes are hardly useful for anything else than loosening up a bit and causing tremendous harm. The only countable deaths LSD ever caused are those from stupid/uninformed people that killed themselves under the influence of LSD, as for alcohol and cigarettes... I don't even dare to guess their death toll. The gap between psychoactive and dangerous doses is so large no one ever managed to die from an overdose of LSD... There are half-legal alternatives in theory but it's just a generally problematic topic when it really shouldn't be.
But I digress, this thread is not for ranting about stupid, senseless and idiotic laws.

So why LSD you might ask, if you haven't bothered researching stuff like psychedelics. Since mankind has finally conducted studies on LSD again after inexcusable scientific abstinence for years we now know that LSD increases connectivity in the brain, which in simple terms means that on LSD parts of your brain are gonna talk to each other that normally don't do so. Ever.
As such the stuff you see isn't gonna be dictated solely by your normal visual input anymore. To come back to the control panel metaphor, LSD temporarily creates tons of new links between different input methods, and some of them will have immediate effect of on your visual perception.
Thus in case of trying to learn seeing things that aren't actually there, LSD helps by doing 2 things.
1. The visual hallucinations under the influence of LSD provide immediate feedback and thus bridge the input-feedback gap you would normally suffer from when sober
2. By linking up a lot more than just the initial part of the brain responsible for vision to your visual perception the array of possible inputs to try experimenting with sharply increases, which means you get a larger sample size to learn from

Now don't get me wrong, I'm not saying LSD is gonna do some wonders and you'll just drop a load, go on a single trip and become superhuman over night.
But I do sincerely believe it can make an insanely difficult task a good bit easier. But it's still gonna be very difficult, and LSD isn't gonna replace researching yourself, and you'll still need a lot of time and practice.

Also, dreams might be able to help with this, but I'm not quite sure how to transfer from dreams into reality and vice versa yet.

How I got the idea for this thread:
Fitting to the main theme of this forum, it was a dream that caused me to think about this again and with this detail. Skipping all the unnecessary details, the dream (not lucid) was about me doing sexual experiments, to be precise I completely separated the link between sexual pleasure and cumming, thus in turn eliminating the refractory period, removing the upper pleasure cap and allowing the pleasure to constantly grow without it forcibly declining after a temporary high. Suffice to say the dream was insanely pleasurable, more so than real sex probably.
If you're male, chances are you're going to know that sexual pleasure is severely limited by the dreaded refractory period. You get a small high of pleasure and then the body just kills off the feeling which is highly frustrating at best. There are techniques to alleviate this problem, usually involving training the CP muscle and preventing ejaculation during the orgasm which also prevents the refractory period. Those are all only physical workarounds however, not solutions to the actual problem.
Given the dream I suspect there is a chance that you could actually learn doing what I did in the dream, in real life. What supports this theory is that once on my life I had a freak occurrence where indeed I had 2 orgasms in insanely fast succession, completely skipping the refractory period from the first orgasm without me ever finding out how or why.
I noticed that the way I attempted to sever this link in the dream involved experimenting with my inner control panel in a way that felt similar to trying to learn visualizing, which is ultimately what brought me here.