Hi vmishra21 ,
660 is a great score and you can surely increase your score to 720+. You should dedicate around 2 months to improve your score. If you study dedicatedly for that period, you are sure to achieve your goal. If you are willing, there are some great GMAT prep companies that can help you with your preparation.
In order to make an informed decision I would highly encourage you to go to their websites and try on their free trial and decide for yourself which one do you like better. You try out free access to EmpowerGMAT,
Magoosh and Optimus Prep as they have great reviews on GMATCLUB.
Also for verbal, I would highly encourage you to consider
e-gmat verbal online or the
e-gmat verbal live course. They are both amazing courses especially designed for non-natives. They offer almost 25% of their courses for free so you can try out their free trial to decide which one you want to go for. Plus the
e-gmat Scholaranium which is included in both the courses is one of the best verbal practice tools in the market. You can easily track your progress in that you can identify your strengths and analyze and improve on your weak areas.
I must add that if you are particularly looking to discover and improve on your weak areas in quant; a subscription to
GMATCLUB tests is the best way to do that. They are indeed phenomenal and will not only pinpoint your weak areas but also help you improve on them.
Further taking multiple mocks might help. Apart from the GMATPREP,
Manhattan GMAT tests and Veritas Prep Tests in my experience have good verbal and Quant section and will certainly help you point out and improve your weak areas.
Further another advantage of taking many mocks is to build up your stamina. Apart from the GMATPREP tests, taking practise tests of any major GMATPREP company ought to do that.
Lastly I would also encourage you to purchase the latest version of
OG and the verbal review for some great additional practice. Here is a link that will help you with your decision.
https://gmatclub.com/forum/best-gmat-ve ... 68383.htmlHope this helps. All the best.