If you were asked to think of something you never thought of before, what would be the most reliable way to do it?
When I read about how most of our thoughts are repetitive, I wondered if it would be possible for us to have a thought that is completely new or original by will. Is there some way we can have unique thoughts whenever we wish to?
Please note that this question does not focus on our brain's mental capacity or free will to be able to think of something original. You could think of it something like asking you to paint something original; I am not asking if you are even able to paint in the first place, but instead how you would paint it if you could.
Also you should ideally be able to think of something new completely by your own in your consciously aware and normal self, without relying on external factors like taking inspiration from your surroundings or words from a recent/ongoing conversations, looking at the content open in your device, using any drugs or consumables, being affected by strong emotions etc.
I'd take two random words/topics, and try to think of something that involves both of them.
For example, I just thought of a bicycle and of curtains. I immediately imagined a person riding a bicycle with curtains stuck in their wheels, getting torn more and more as they tried to cycle away. That's a thought I don't think I ever had before.
Maybe try different directions. I just tried and imagined a giraffe nudging a fried egg off the roof of a car on a hot day. The heat and how it sears fur on your face is a different thought from someone riding a bike with wheels caught in curtains because the bike idea is more visual and emotional (frustration, probably) and the giraffe one is more physical (heat).
I think the best way to think of something new (to you, something new to all of humanity is harder of course) would be to pick some aspect of society, your daily life, a technology or social norm you are familiar with,... and analyse which underlying assumptions make it the way it is and then just figure out what would happen if that assumption didn't hold. That is basically what a lot of classic science fiction writers (among others) did. Take e.g. Asimov's Nightfall, a story about a world with (IIRC) 6 suns where it is only night once every 2000 years so people are not accustomed to darkness at all. Or Terry Bisson's They're Made Out of Meat where he questions our implicit assumption that aliens would be meat creatures like us.
Or - drugs. Drugs are good too. I don't know why you're applying these artificial constraints to this problem as if there is some notion of "purity" or "cheating" to the practice of idea-generation. Is an idea any less worthy, insightful, or useful because you came up with it while using a chemical tool to do so?
Even then my hallucinations were informed by memories and events from my life, people, or sounds.
It's hard to even know if seeing pure geometry is an original thought. I don't actually think a truly original thought is possible. Everything takes from everything else, in some small way, and builds on it.
Also you should ideally be able to think of something new completely by your own, without relying on external factors like taking inspiration from your surroundings or words from a recent/ongoing conversations, looking at the content open in your device etc.
If it could be expressed in existing ways, would it still count as entirely new or unthought of?
Regarding your last paragraph, I don't think I could do it. I can't think of a single time that I have thought of something I've never thought before where it hasn't been catalysed or at least shaped by external factors.
So to answer your question without that constraint, I've found good success in actively seeking out viewpoints that are different to mine. Some years ago, for example, I was a leftist who felt like ACAB was unreasonably inflammatory and "surely not all cops". I googled something like "Why ACAB is true", and found some compelling arguments. I tried to then debunk those arguments by trying to find evidence or reasoning against them, and I continued in that way for a while, and now I'm an anarchist.
It took a long while to get to the point of identifying as an anarchist, but the ACAB thing was a great example of what caused me to think in a way that was novel to me.
If we are talking about thoughts that are original not just with respect to me, but the wider world, I've found good success in reading outside of my field. I'm a scientist at heart, and I have studied biochemistry to a graduate level. That's the main field I work in. I'm a very stereotypical, systematic scientist, and that means I've not had much exposure to art or literature or other parts of the humanities.
I've been learning linguistics recently and there have been a few times that the way I have understood some core concept is distinctly different and perhaps even surprising to how my linguist friends would see it. Not wrong, just different. Everything I have learned is shaped by everything I've learned before, so I've found a lot of value in diving into fields that are outside of my wheelhouse.
Sometimes, I find concepts or methods that I don't understand well enough to say I know them (without more work), but even those are useful to me. They make me think in a way that is unfamiliar to my scientist brain, and that makes me more likely to have thoughts that no other scientist in the conversation has thought of before.
I've found a lot of utility and fulfillment in leaning into having a wide but not especially deep pool of knowledge surrounding my primary domain. I wish I could learn all of the things much more deeply, but I've come to appreciate the power of the paddling-depth water surrounding my main area.