Critical thinking refers to the ability to assess information and viewpoints through thinking, reasoning, and analysis. It is crucial when writing English essays as it helps to better understand the main message and the intentions of the author, as well as to effectively express one's own opinions and thoughts. Here are some methods to foster critical thinking skills:

1. Read a variety of texts from different genres, including news, technology reports, literary works, and more, to cultivate the ability to think critically.

2. Learn to ask questions about the viewpoints and arguments presented in texts. Constantly query with "why," "how," and "is this correct?" to delve deeper into understanding the article and the author's intentions.

3. Develop the skill to gather and organize information, comparing and analyzing different perspectives and evidence to form your own opinions and judgments.

4. Nurture logical thinking abilities and learn to analyze and reason, organizing your viewpoints and evidence in a more rigorous and persuasive manner.

5. Practice expressing your own viewpoints and thoughts. Through writing and speaking, translate your critical thinking skills into practical actions.

In summary, critical thinking is a skill that requires continuous exercise and improvement. By reading, thinking, and expressing continuously, you can gradually enhance your critical thinking skills and, consequently, write excellent English essays.