Some great advice here but the path is pretty simple. If you already have a basic education, begin by studying highschool algebra, trigonometry, science, and calculus. You probably overlooked or have been fatigued by these subjects already because we live in a society that has begun to think of them as useless. Do thousands of problems. They will cumulatively rewire your brain until you are a critical thinking machine. Bonus, continue studies to college-level mathematics, physics, engineering, and chemistry. Start here https://www.khanacademy.org or utilize other free resources that are abundantly available online. Challenge yourself and enroll in a university or community college. Understand, there are no shortcuts. Start with the first rudimentariy problems and concepts you already understand then progress slowly and orderly from there.

Push yourself as far as you can for as long as you can. If you are serious about the development of this skill, give yourself a few years. Take breaks when necessary and don't let failure deter you. The pay off is a mind capable of critically handling most problems life can throw at you. You will ultimately realize the only real aggregate difference in pay and job security is whether you chose a field involving math or not. The fact is, much to the chagrin of the meme lords calling these courses useless, math is the only real important training an education can provide. An unshakable foundation of the mind. Common sense unfortunately cannot be taught but it is not true for critical thinking.