Thoroughly research the topic. Your essay should provide enough in-depth information about the subject that you come across as an expert. That means digging deep. Spend time learning about the writer's work. If he published more than one work, compare and contrast his themes and styles from book to book. Spend time learning about the writer as a person -- childhood, other occupations and avocations, personal affiliations.
Choose a thesis. Your thesis is the main idea that all of your arguments and evidence revolve around. It is the idea your readers will focus on as you share your ideas and back up your claims. Your thesis should line up the writer's background and common themes in her work. You can also explore why certain themes reccur.
Analyze the arguments you will present to the readers. The knowledge that you gather from your research will serve as a strong foundation upon which to build those arguments. The arguments need to be sound, logical and clearly defined. Make sure the reasons and evidence are clear and make sense. Carefully look out for any weaknesses in your claims.
Create an outline. An outline will help you organize details about the author's life and the ideas you develop about them, so that you can communicate them clearly and logically. Your outline doesn't need to be anything formal or complicated. It can be as simple as a series of one-line sentences describing what will be covered in each paragraph. It will map out the essay from start to finish.