How do I write critically in an essay?

While mentioning limitations of research and theory is good, simply listing them does not show criticality. It is important to consider why limitations such as 'low ecological validity' are significant, specifically for the topic or piece of research that you are evaluating. Why does it matter in that particular instance if research has low ecological validity? Another way to write critically is to consider why the findings of research are important; discuss the relevance to the theory and consider why and how researchers may have found the results that they did. Mentioning real world applications also shows wider thinking and that you can extend the reading you've done to see how this may affect society/practices/treatment, etc.