Hi there,
A verbal score can be improved but I have absolutely no specifics about you. Of course the main advice is to study. However, without knowing your level, your previous study technique, etc, it is difficult to simply give advice. Firstly, you need to learn how to attack the Verbal section. This means you need to learn what every question type is and what the appropriate technique is for mastering such questions. Every single question has a line of attack and it is up to you to learn how to attack it so that you become more precise, faster, and learn how to filter out information you do not need to see.
Once you learn the proper technique and associated traps for the question types, then you must practice utilizing that technique in the same way you learned it; you must become systematic in your approach to every question so that no matter what they throw at you, you will already have seen it countless times before. Along with the practice of questions on an individual level, you will also need to practice exams that are at the same level as the real GMAT, and you will have to analyze these deeply so that a clear picture emerges about your remaining weaknesses and how to overcome these and how to form a proper timing strategy for test day.
Altogether it comes down to utilizing a technique that works for you, practicing such a technique on individual questions and exams, and of course asking questions when you have them! You got a 660 which is good, but to get to a 720 there is obviously some fine tuning which needs to take place and if it is a question of gaps in knowledge (for example certain redundancies or changes of meaning in the SC or falling into traps in harder RC Application questions, etc.) then these specific gaps obviously need to be addressed and practiced because these are the small things that most student fall.
learn properly, practice well, and good luck to you.
