Read essays written by other authors. Visit the school library or public library and go to scholarly websites such as JSTOR and Project Muse for articles on English-related subjects. If the essay will require you to analyze Shakespeare's works, look at essays on Shakespeare and see how other writers have successfully approached this subject.
Read newspaper or magazine articles and formulate three questions about them. Answer each question with short paragraphs. This is a good way to practice analytical writing and critical thinking, which you'll need for the exam.
Practice your grammar. English essays require adherence to proper grammar, so it will be important to reacquaint yourself with sentence and paragraph structure, parts of speech and vocabulary definitions. Turn to grammar books and dictionaries such as the Merrill-Webster Collegiate Dictionary for help.