Thoroughly read the topic. Just because you are given a limited amount of time, do not quickly skim through the question in order to race the clock. Part of doing well on the analytical writing section is being able to fully understand what the question is asking you. Devote a couple of minutes to thoroughly read the question and jot down a few response ideas before you continue with the writing.
Offer supporting details. Do not simply write an opinion piece. Support your argument with clear examples and evidence. For instance, if the topic asks you to discuss the effects of global warming on the polar bear population, consider the evidence available that can either support this claim or debunk it. If you are able to recall any scientific evidence from a past biology class, use it.
Study vocabulary. In order to help you expand and sharpen your vocabulary skills, study suggested GRE word lists. Memorize definitions and, most importantly, spelling. You can find free vocabulary lists online. (See Resource.)
Proofread for errors. If you finish your writing section with a few minutes remaining, do not be so quick to move on to the next section. Use the remaining minutes to carefully proofread your response. Review for grammar and spelling errors, double-check that you used appropriate evidence and that you didn't veer off into different topics.
Access extra help. For a fee, you can purchase helpful study tools that offer practice questions and writing exercises tailored especially for the GRE and analytical writing section. Some recommended resources include the Kaplan or Barron's GRE preparation books.