GRE

Hello Rahul,
There are some basic principles for people who are trying to prepare on their own. Crafting studying technique is something more tactical, and personal, that you'll have to do on your own, based on what you know about how you best learn. Most of these, apart from distinctions as noted, apply to standardized tests in general:
Start by creating a realistic schedule of daily work. Because the daily part is important, realistic probably translates to 15-20 minutes a day. I am going to spend two hours a night is well-intentioned, but unlikely to happen. Use only the official materials. There is only 1 published book for the GRE.
Materials include practice problems and practice tests. Do the practice problems first, then do regular practice testing as the actual test date approaches. There are two official GRE practice tests that are free to download. Because the tests are adaptive, they can be taken multiple times. You can get away with around three sittings per test without significant overlap, so that allows you six practice tests. These should be taken once a week for the six weeks leading up to the test, in an environment that simulates the actual testing environment as closely as possible (e.g., wake up and start the test at the times you would need to, isolate yourself in a distraction-free room, don't let yourself listen to music, put your phone somewhere else).
Though there is no official vocabulary list, GRE preparation requires studying vocabulary. Antonyms and analogies (and, to a lesser extent, sentence completions) lean much more heavily on sheer vocabulary than the passage or vocabulary in context questions that have largely replaced them on tests like the SAT for precisely that reason (see how have the SATs changed over the past 20-30 years?). They comes far closer to being you either know it or you don't. Fortunately, there are a lot of vocabulary books out there, and just doing a little every day increases the odds that you'll get these questions correct.