After reading the question, begin to brainstorm. Decide on the topics to address quickly, within the first three minutes. Then, begin to write. Know how to use transitional phrases, introductory and conclusion paragraphs, as well as vocabulary to attack an argument. Many of these phrases or words can be written on the scratch paper before the exam begins.
Time management is always a concern.
Bear in mind that GMAT is computer adaptive. On the multiple-choice sections, getting the first questions correct is critical. There is a variety of material both for sale and on the Internet to help GMAT professors. ARCO publishes an excellent text, Teach Yourself the GMAT CAT in 24 Hours . We think that the Princeton Review's GMAT book is not as thorough as ARCO's, however, it includes an excellent CD-ROM with exercises and practice tests.