Farnam Street is my favorite blog about it. I would recommend 3 articles:
-- Second Order Thinking - https://fs.blog/second-order/
-- Implications of Second Order Thinking - https://fs.blog/2020/03/chestertons-fence/
-- How to Think - https://fs.blog/2015/01/thinking-about-thinking/
This should be a great start on how to improve your critical thinking skills. Then, I would explore decision-making biases and how to avoid deal (by yourself or in a group).
I believe you can find some free online resources if you search for critical thinking or systems thinking.