Define a topic: If you`re allowed to choose your own topic, try to pick something that you already know a bit about and that will hold your interest.
Some students react to the time pressure of essay exams by scribbling down their introduction as soon as they`ve read the question and figuring out their points as they go. While it might seem counter-intuitive, taking five or ten minutes before you start writing in order to draw up a plan will be an enormous time saver.
Understand your assignment: What is the goal of this essay? What is the length and deadline of the assignment? Is there anything you need to clarify with your teacher or professor?
Although the conclusion paragraph comes at the end of your essay it should not be seen as an afterthought. As the final paragraph is represents your last chance to make your case and, as such, should follow an extremely rigid format.
However, this thinking process does not reflect the reality of the situation. In fact, even if your teacher hasn`t given you any hints about the essay question, you do know what it will be about: the concepts and ideas you`ve discussed in the course.
Do your research: Read primary and secondary sources and take notes to help you work out your position and angle on the topic. You`ll use these as evidence for your points.