Hi ArsalanS,
Since it sounds like you're just beginning your studies, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can download 2 for free from
www.mba.com (and they come with some additional practice materials). If you want to do a little studying first, so that you can familiarize yourself with the basic content and question types, then that's okay - but you shouldn't wait too long to take that initial CAT. That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 4 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can come up with a study plan.
Early last week, GMAC made a formal announcement defining some changes that will be taking place to the format of the Official GMAT (beginning April 16, 2018). These changes primarily impact the overall length of the Exam (meaning the number of questions in the Quant and Verbal sections as well as the amount of time that you'll have to complete each of those two sections). In theory, a shorter Exam could make it easier for a well-prepared Test Taker to score higher. Unfortunately, practice CATs in the new 'format' don't exist yet - but once they become available, you should plan to switch over to those shorter CATs during your studies.
I'd like to know a bit more about your timeline and goals:
1) What is your goal score?
2) When are you planning to take the GMAT?
3) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich