I think that there are some general guidelines to stick to in any formalized writing assessment. The links below will help in providing detail along these lines. I would stress that my experience has indicated to me that there is no substitute for reading the prompt and clearly outlining what needs to be answered in your essay. The idea of having a plan and making sure that your writing reflects it will ensure that your writing is streamlined and not "off book" as you compose your work within a time setting. At the same time, I think that making sure that your outline includes specific textual evidence or references to answer the question will be critical.