Critical literacy comes from a strong foundation of knowledge the ability to actively read, analyze and critique new information. Active reading is the crux of your dissertation, so you need to spend time in your doctoral program practicing these skills. To begin reading with critical literacy you should skim a text to get a thorough understanding of the topic.
Read the titles and headings, understand where the authors are coming from, read the summaries and conclusions and decide what big questions you expect the article to answer. While you keep those questions in mind, jot down the main concepts that you come across in the reading. If your main questions are not answered, that is something you can include in your critique of the article.
Unanswered questions may also help you to find additional research or to formulate your own hypotheses about the topic. When you are finished reading the article and reviewing the information, give yourself time to process the information. After this, write a summary of what you learned and what lingering questions you still have. Finally, read several more texts on the topic so that you can compare the way authors present the information.