As with most things, awareness is the first step. Students must be aware of critical thinking and what it is. These days, with the idea of fake news so prevalent, it is quite easy to use that term to introduce and explain the concept of critical thinking. This is an easy and persuasive image to introduce the idea that “just because it is on the Internet doesn’t make it true.”
I teach students that you must develop digital literacy, an understanding of how to determine whether something you see online is true or false. For lower-level students, I start with the 5 Ws and 1 H questions. Simply ask a number of these questions to find out if you are seeing/hearing fake news.
There are tons of examples, articles, and lesson plans online about critical thinking. Google search “critical thinking EFL students” and you will find more than you can ever use.