To avoid the various foolish opinions to which mankind are prone, no super human genius is required. A few simple rules will keep you, not from all error, but from silly error.
If the matter is one that can be settled by observation, make the observation yourself. . . .
If an opinion contrary to your own makes you angry, that is a sign that you are subconsciously aware of having no good reason for thinking as you do. . . .
A good way of ridding yourself of certain kinds of dogmatism is to become aware of opinions held in social circles different from your own. . . .
Be wary of opinions that flatter your self esteem. . . .
-Bertrand Russell, from his 1943 essay An Outline Of Intellectual Rubbish, which is reprinted here