Many levels and types of schools try to teach "critical thinking". I just looked up the term and I find definitions and examples that don't always match. I take critical thinking to be thinking critically, trying to notice statements that don't seem to ring true, statements that seem to contradict one's own experience, statements that are not supported by evidence. I find it helpful to state ideas or assertions in clear English and then ask Byron Katie's question: "Is it true?"
So, where do I get this common wisdom? Where do I find the widely accepted ideas that make up common truths, accepted notions? Ok, there is no one place. But you can look. You can make a list of what different news sources, books of philosophy, what comes to mind from memories of your childhood and your parents and grandparents. I find a major clue is repetition. When something gets repeated often enough that you notice that you have heard or read that before, you have probably uncovered a bit of commonly accepted information.
It says in Ecclesiastes to try hard. Ok, it actually says in the King James Bible: "Whatsoever thy hand findeth to do, do it with thy might." My experience is that most parents, coaches and uncles and aunts agree: Work hard.
So, apply critical thinking. What if I don't work hard? What if I work soft, easy, lightly, sporadically, sloppily? If you think about it, you may find things you have accomplished, or found or achieved that you didn't work at but which were a success. Many thinkers have found that considering the opposite of accepted ideas can result in being ridiculed, disliked, ignored. It can certainly happen that a thorough evaluation of an accepted idea shows that it is an excellent principle, one that you support yourself.
Two of the most commonly spread ideas I run into today are
The US is in trouble because of overly deep political divisions
The earth is in trouble because of overheating, overpopulation of humans and their activities
