From my experience, coaching classes in India are doing pure business and making money. In most of the coaching classes in India one will found faculties claiming that they scored 700+, that their grammar concepts are 101% clear, and that one is at the right place for GMAT prep, but sooner or later one realizes that faculty don't even know the depth and breadth of GMAT. If you are joining any GMAT classes ask institute to provide score card of faculty, no need to shy because it is better than wasting your money and time. Poor guidance at early stage is the root cause behind multiple year + attempts in GMAT. Most of the people realizes what GMAT is exactly only after their first attempt. Therefore, element of self study must go independent of coaching classes, and do not 100% rely on what coaching classes claim. "Gmat is not halva (cake walk)"
Further, if one wants to go ahead with self study or group study, then I would recommend for practice
OG and GMATCLUB and for specific topic such as SC take
MGMAT SC,
MGMAT verbal foundation, and
e-gmat SC package, CR take powerscore, a best CR diet, and RC there is no as such straight forward resource to improve accuracy -- some people opt note making technique to improve accuracy and compromise speed. For Quants, gmatclub has best gurus and resources available on earth, so just practice as much as you can.