Familiarize yourself with the test format and the types of questions in each section. Go to the official GMAT Web site and read through it thoroughly. Additionally, download the free test prep software available on the site. Obtaining GMAT study books by either purchasing them or checking them out from the library would also be helpful.
Review the materials on the GMAT test prep software and, after taking the diagnostic tests, make a list of your weak spots. Create a four-week-long study plan for yourself based on the evaluation, making certain to take extra time to strengthen your weakest areas.
Go over the sample questions for each section of the test until you feel familiar with the types of questions asked and understand the strategies used for solving each type. Make sure you understand any mistakes you made on missed questions.
Practice for the analytical writing analysis by studying sample topics on the official GMAT Web site. You can purchase official GMAT software to practice the writing section or enlist someone who is skilled with composition. Another option is to contact the writing lab or student resources center at the school where you received your bachelor's degree for tips.
Become familiar with the types of critical reasoning questions that appear on the test. While they make up a relatively small proportion of the test they often stump those who have not studied specifically for them. By understanding the general format of the questions and the types of answers likely to be correct you'll have a much better chance of answering correctly.
Review basic math skills if this is not a strong area for you. Don't worry about higher level math like trigonometry or calculus. Focus on high school arithmetic and geometry. Word problems are the most widely used on the GMAT, however, no GMAT problem should require lengthy calculations. One problem solving technique is to work backwards, using an answer in the problem to see if it works. If not, then plug in the next possible answer.
Remember to take an occasional day off from studying. If you become overly stressed and mentally burned out you'll not do well on the GMAT. Make certain you get plenty of sleep the night before taking the GMAT.