Preparation is essential if you plan on taking the Graduate Management Admission Test (GMAT). Being ready to answer all GMAT questions increases your chances of earning a high score. Generally, GMAT questions come from two broad categories: mathematical and verbal. Some GMAT prep study guides focus one or the other. Other excellent study materials for prepping for the GMAT include practices tests and websites.Study GuidesMany companies publish study guides for the GMAT. The Graduate Management Admission Counsel (GMAC) publishes the most widely used study guides called the "Official GMAT Study Guide Series." These study guides give sample mathematical and verbal questions with tips for every section of the GMAT. These official guides are available in electronic and print format from the GMAC website.Practice TestsFor test takers, practice tests can be quite valuable in preparing for the GMAT. Practice tests quiz students with questions once used on real exams. This gives you the opportunity to master the format of the test before you take it. A number of sources make GMAT practice tests available for studying. The GMAC provides test preparation software with the largest inventory of questions, answers and bonus materials to assist you in preparing for the GMAT. Other unofficial websites have smaller portions of the exam available for review that cover different sections of the GMAT.Home Study CoursesMany organizations offer comprehensive study courses for home. Usually, these courses consist of a notebook, textbook and a set of DVDs. These home courses can be quite expensive (in the hundred of dollars), but provide an in-depth review of GMAT questions over any other conventional GMAT study books. The leading company selling GMAT home study courses is the The GMAT Coach. Their materials can be purchased from their website.Math and Writing BooksGMAT questions are not intended to be esoteric. Rather, the exam evaluates basic mathematical and verbal reasoning skills used in similar college science and language courses. In addition, non-specific GMAT study books, math books, dictionaries and English grammar textbooks can be especially helpful with preparing for the GMAT. Math books should cover geometry, algebra and arithmetic. English textbooks should cover critical reasoning, reading comprehension and grammar.WebsitesSeveral websites provide free advice for studying for the GMAT. These websites are not GMAC officially approved resources, but some are still well regarded by professionals in the field of standardized testing. GMAT prep sties like Kaplan, Veritas and Princetion Review post some information from their classes online that can be used for individual study sessions. Also, there are websites that have been started by individual students to help other students prepare for the GMAT through useful tips and hints.