This is in response to a challenge. I am not saying here I am a great thinker. On the contrary, because I wanted to learn how to improve in my decision making in all areas of life, I started a podcast. I've spoken to around 1300 great thinkers and I've been so impressed with them and also have found many things in common.

1. An enormous amount of knowledge
Before having a "vision" of the future, whether it's a basic decision or an opinion about where things are going, many of these people (all of them) have an enormous ENORMOUS amount of knowledge about many many subjects.
Most of it is through reading. Some of it is through experience. A lot of it is very directed reading, so they learn everything about a topic.
But they also make sure they read about completely unrelated topics so the synthesis of the topics (idea sex) happens in their heads.
When they get the knowledge through experience, it's still often backed up by reading, by mentors, by going through some hard time and persevering through them (although this is not a requirement).
And in order to remember a lot of knowledge, you have to love what you are reading and have great curiosity about it.
Part of having love for what you are reading means you aren't reading textbooks but are often reading very good writers. It also means reading and experiencing enough to figure out what things you love to learn about and you don't.