The first step is to learn to ask the right questions: Who is making the claim? What are their credentials? And what might be their motives to make me think this? What are the premises of the claim? And how might they be flawed? What are my own initial assumptions? And how might they be flawed? What are the alternative explanations for their claim? What is the evidence? And how does it compare to the alternative explanation? What further information do you need before you can make a judgement?