The current GRE's sections on verbal and quantitative reasoning are scored on a scale of 200 to 800 in 10-point increments. The analytical writing section is scored on a scale of zero to six in half-point increments. In August 2011, ETS will begin administering a revised GRE with a new scoring system. The analytical writing section scoring will remain the same, but the verbal and quantitative reasoning sections will be scored on a scale of 130 to 170 using one-point increments. As the revised GRE is not yet being administered, schools that provide GRE data are still reporting scores that use the current scoring system. Be sure that you are using the appropriate scoring system when comparing your test scores to suggested scores.
While most graduate programs do not require applicants to achieve a minimum score, there are many opinions as to what constitutes an acceptable number. According to GRE Explorer, it's best to have at least a 550 on the verbal reasoning section and 700 on the quantitative reasoning section. Jumbo Tests says that applicants should aim for scores that are above nationwide averages, which it reports as being 460 for the verbal reasoning section, 590 for the quantitative reasoning section and 4.0 for the analytical writing section.
Look on the websites of the graduate-school programs that interest you to see if they include information about past incoming classes' average GRE scores. This will give you an idea of what scores may be expected, but getting lower scores does not necessarily preclude you from admission. For example, the University of California, Berkeley reports that past applicants to its English Ph.D. program have had scores in the 700s on the verbal reasoning section. Schools look at an applicant's entire application when making admissions decisions. It is possible to balance out a low GRE score with an outstanding grade-point average, personal statement, resume and letters of recommendation. Low scores do not automatically disqualify you from being admitted, just as high scores do not guarantee admission.
Some schools provide ranges of scores that past admitted applicants have earned instead of reporting averages. This information will help you determine whether your scores fit into the range and, if they do, whether they are in the upper or lower parts of it. If they do not, you may want to take the GRE again to try to improve your scores, or you may want to ensure that the other components of your application are especially strong to compensate for them. Some programs, without calling them minimum scores, provide the scores that they consider to be low. Harvard University's Graduate School of Education specifies "significantly low" scores as being less than 460 on the verbal reasoning section, 580 on the quantitative reasoning section and 3.5 on the analytical writing section.