I think that the most important things to remember are: correct grammar and good vocabulary, who your audience is, and to have a good, strong thesis statement. I found that putting your essay paragraph by paragraph into Google Translate and listening to it will help you catch small errors that you might not have realized were there when you were reading it. I know it seems childish and redundant, but making a flow chart/any other kind of map will allow you to focus on your ideas one at a time to ensure that your essay is organized and well though out. Good luck!