It is advisable to take approximately 3 full months of preparations for this test. Those who have poor or vague knowledge in required disciplines should take not less than 6 month of preparation.  Several private institutes offer short term courses for GMAT preparation.

These institutes offer two different types of courses for GMAT preparation:
- GMAT online course
- GMAT classroom course.

Online courses are best for those who cannot attend classroom courses for some reasons.

Those who choose classroom course for GMAT preparation should make out first the university special computer test supply availability. There are some peculiarities in taking for example GMAT CAT (computer aided test) that consists of 4 sections and lists for about 3 and a half hours.

Section	Analysis of Issue Essay	Time
Writing	Analysis of Argument Essay	30m
Writing	Analysis of Issue Essay	30m
Math	37 questions	75m
Verbal	41 question	75m

The test usually begins with writing task, which is performed by the test taker on the computer. Each question must be answered before you can go to the next question. Further, you cannot return to a question once you go to the next question.

Approximately 25% of the GMAT CAT questions are of experimental character; among them you can find math problems, data sufficiency, reading comprehension and sentence correction. But you don’t know what the questions are experimental!

Every new GMAT has almost the same level of difficulty as the previous one. The experimental questions measure the relative difficulty of potential questions; if responses to a question do not perform to strict specifications, the question is rejected.
   
Many students discouraged by answering GMAT experimental questions show poor results in other sections of the test.  Some testing companies are becoming more enlightened in this regard and are administering experimental questions as separate practice tests.
 
Knowing that the experimental questions can be difficult, if you do poorly on a particular question you can take some solace in the hope that it may have been experimental.

If have done the number of questions quite badly, you may hope at least that they were experimental. In other words, do not allow a few difficult questions to discourage your performance on the rest of the GMAT.