Before you start writing, you should make sure you have a clear idea of what you want to say and how you`re going to say it.
Consider practicing writing under time pressure. You`ve probably written dozens of essays before–the only thing that sets a timed essay apart is that it`s timed. Students often struggle to complete the full essay within the time constraints, particularly if they have to write longhand when they`re accustomed to working on the computer.
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.
For this reason, it can be helpful to simulate the conditions of a timed exam before the actual day: pick a practice question, find some lined paper, set a stopwatch, and see how you do!
Therefore, if you take the time to review your notes and ensure you understand everything that was discussed, it should be difficult for the essay question to catch you off guard. As soon as you read the question, relevant course concepts will start popping into your head, and you`ll just have to organize them into a coherent essay.
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.