Become familiar with the course content. If the professor hasn`t told you in advance what a timed essay prompt will be, it can be intimidating to think that you will have to write about a subject you`ve never seen before.
Start planning if you can. Although the situation described above sometimes occurs, it`s also very common for professors to give their students a fairly detailed idea of what an essay question will involve in advance of the test day.
However, it`s important to keep in mind that your professor understands the circumstances under which the essay was written. They`re fully aware of the time pressure you were dealing with, and they will judge your work far differently than they would judge a typical essay with a deadline set weeks after the assignment date.
Create an outline: Map out the rough structure of your essay in an outline. This makes it easier to start writing and keeps you on track as you go.
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.
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.