Sorry to disappoint but quality of your decisions grow only proportional to your expertise in some area.
There are adjacent and similar areas, so by getting better at one you improve your decision making in others as well.
But any book that tries to sell you generic “decision making” skill is a piece of garbage.
This is how skills work fundamentally.
Meta-skills cannot be learned, can’t be trained. This is why they are meta
Focus on exact narrow areas (even “startups” is way to generic, “startups fundraising” or “hiring in startups” are better examples) you want to improve.
And slowly (with life experience) you’ll build up a good intuition in those areas. But don’t expect it will help you be great in other distant fields. Though it may happen by accident or because you’re generally smart enough to avoid mistakes.
Also nobody likes this answer, but religion writes the manuals to life. All major religions have done their research and wrote books. There's a stark contrast between ancient Greek philosophy to when Christianity came in. There were unsolveable problems that the philosophers couldn't tackle, like Aristotle believed that if a great made a mistake they were done for. And then Jesus came in with the idea of repentance and flipped this on its head. The word "hamartia" changed from "missing the mark" to "sinning", and sins are recoverable.
Then Islam based the ideal lifestyle around every behavior and action by the Prophet Muhammad, from sleeping, headaches, eating, treating guests, treating enemies, and so on. Philosophy became necessary because later there would be scenarios where there was no precedent for decision making, so they wanted analogies. Aristotelian philosophy became a tool for this. Then you had Avicennian philosophy, which developed into inductive logic... things we take for granted today like symptoms. Then al-Ghazali came in and labeled all of the philosophers as nonsense, and Greek philosophy was buried until the 19th century.
So if you want a tldr, read al-Ghazali. His big work was Tahāfut al-Falāsifa ("Incoherence of the Philosophers"), but if you want something simpler and much more practical, try Ayyuhal Walad ("Advice to a Son/Student"). It's hard to find an English translation that properly captures the sarcastic bite in his writing though. Plenty of religious figures were funny and sarcastic too.
Honestly, as a society, I think we've gone full circle. We're rediscovering meditation/mindfulness. Which is a fair point - approach all decisions from a fresh mind. But that works up to a point. There's just so much that it takes a while just to go over what to cover and what not to cover.
As an overview and primitive generalization of some more or less obvious ideas about human nature to read for fun - good enough.
As a real learning tool - garbage.