Spend a few minutes before starting to write brainstorming and coming up with the main idea you want to convey. Formulate a theme and state it clearly, write two or three paragraphs expanding on and supporting the theme, then write a concluding paragraph with a summing up and reiteration of the theme in new wording. Once you have the theme and the format clear in your mind, it should help you to pound out the essay more quickly. Also, if you have said all you need to say, it may not matter if it is a little shorter than what you would usually write. Get one whole “draft” of the essay finished, and then if there is still time, go back and revise and polish it.