Why do we need to take a critical approach to reading?
Regardless of how objective, technical, or scientific the subject matter, the author(s) will have made many decisions during the research and writing process, and each of these decisions is a potential topic for examination and debate, rather than for blind acceptance.
You need to be prepared to step into the academic debate and to make your own evaluation of how much you are willing to accept what you read.
A practical starting point therefore, is to consider anything you read not as fact, but as the argument of the writer. Taking this starting point you will be ready to engage in critical reading.