The best way to ensure that you will do well on essay exams is to keep up with readings and assignments from the very start of the course: Do the reading, go to lectures, take careful notes, participate in discussion sessions, and organize study groups with classmates to explore and review course material throughout the term. Trying to cram weeks of information into a single night of study will never allow you to do your best.
As you study, avoid simply memorizing information aimlessly. Instead, clarify the important issues of the course and use these issues to focus your understanding of specific facts and particular readings. Try to see relations among topics; concentrate on the central concerns of each study unit, and see what connections you can discover; and place all you have learned into a meaningful context.
As an exam approaches, find out what you can about the form it will take. No question is more irritating to instructors than “Do we need to know this for the exam?” but it is generally legitimate to ask whether the questions will require short or long answers, how many questions there will be, whether you may choose which questions to answer, and what kinds of thinking and writing will be required of you. Some instructors may hand out study guides for exams or even lists of potential questions.
If yours does not, make up questions you think the instructor might ask and then plan answers to them with classmates. Returning to your notes and to assigned readings with specific questions in mind can help enormously in your process of understanding. The important thing to remember is that an essay exam tests more than your memory of specific information; it requires you to use this information to demonstrate a comprehensive grasp of the material covered in the course.