Some of the necessary skills are common knowledge. I will list some of them here and you can learn them via any medium you like;

• How to interpret and analyze financial statements (cashflow statements, balance sheets, profit & loss statements, tax laws and so on)
• Basic micro-economics
• Human psychology and social behavior
• Cyclical nature of markets from history
• Study risk, luck and probabilities.

These are certain skills that you need to learn from various sources and deliberate on them.

However, there is certain category of skill that you many not be able to learn from books and it will only comes through personal experience. And that is the ability to call BS and not BS when you come across stuff. The problem with modernity is that the media and news want to make every problem your problem. Most of the sensationalized news information that gets printed and broadcasted has no consequential impact to the world.

Do not consume main stream news like everybody else by learning to filter the facts from BS information. 90% is BS and only 10% of it is factual information.

By focusing on data that is factual and using that data to frame a view point that is the most objective is one of the best skills you can have. Because if you do not have this skill, you will be swayed from one point to another by media, influencers, experts and anybody with an opinion.

Lastly, I must add that you must find other people who are willing to find the truth in a disciplined and objective manner so that you can test your views and refine them. Because, to remain objective by yourself is one of the most difficult things to do.