Hi! I just recently wrote an essay on this book. At first, I also didn’t know how to approach it. But then I came across a very useful resource – https://www.ozessay.com.au/blog/of-mice-and-men-essay/. It clearly describes the most common themes, how to reveal loneliness, dreams, friendship, and so on. I was especially helped by the fact that it explains how to build a structure - an introduction, the main part, and a conclusion. There were also examples of how to analyze the behavior of the characters. I chose the topic of the American dream and why it did not come true for them. It even turned out interesting. I advise you not to be afraid to start - just write down what you remember in the book, and from there, build your reasoning.