There would be two answers for this. In my opinion, if you are confident about your QA and verbal there is no need for you to take coaching for GRE.
A self-prep for 3 months would be of great help to get you the desired score. I think you should start by giving a mock GRE Manhattan prep test. It is free of cost and would help you greatly to understand on which level you are right now and how much you need to improve. I would also suggest you should start searching for free resources from GRE prep there are plenty of them available online. There are at least 4–5 very good free mock GRE tests that you can give like official ETS also gives 2 free mock tests, Kaplan, Barron, Princeton Review and many more. Keep giving all of them as you prepare. Give official ETS practice tests in the last when you are confident. Their result is quite accurate and approximately matches your final GRE score. Practice tests always help and give you a good understanding on the areas you need to improve.
However, if your basics or fundamentals in both verbal and quants are not strong, then we would advise you to spend some time building up the required base and then look forward to good coaching institutes to boost your knowledge and test skills. At a good coaching centre, you can clarify your doubts and learn some more easy tricks from experienced teachers to crack GRE examination. You could also take lessons from your peers who have cleared GRE with high scores and even seek guidance from expert tutors or professionals.