The 12 Virtues of Rationality – A magnificent 2-page read that drags all the self-deceptions at the edge of your consciousness out into the light, names them, and invites you to reflect on them.
Lesswrong.com – The human mind is born flawed. Lesswrong has compiled much of the research done on specific human flaws, as well as how to defeat them. Lesswrong is the most powerful path I know to quickly establishing a broad foundation for clear thinking.
Benito’s Guide lists some of the beginning sequences.
If you’ve ever not known quite how to say what was wrong with a certain line of thinking, or what was wrong with (almost) the entire field of philosophy, Lesswrong is for you.