Hi nishantdoshi,
You don't have to make any big decisions about your Official Test Date just yet (you can always reschedule it as needed or retake the GMAT 16 after you take it for the first time). If you want to choose a Test Date and officially schedule your Exam (so that you can 'lock in' the date), then that's fine though.
The GMAT tests the same general Quant/Verbal concepts again-and-again, along with some overall 'tests' of your critical thinking skills, organization, pacing, etc. ALL of these things are predictable, so beyond learning content (math and grammar rules), you also have to learn the patterns, logic, Tactics, etc. that this Test is built on. Ultimately, YOU are responsible for your own performance, but you CAN learn a lot about this Test (and train to face it) before you actually take it.
While you can begin your studies with the books that you have, many Test Takers get 'stuck' at a certain scoring level when using a 'book-heavy' study approach. As such, you'll probably want to invest in a GMAT Course of some type (either Guided Self-Study or instructor-led).
GMAT assassins aren't born, they're made,
Rich