Hi Swati0993,
Since your verbal scores are inconsistent, its a sign that you have some lingering weaknesses in SC, RC, and CR. To help build your verbal knowledge and find your weaknesses, you should strive for linear and targeted learning and follow that with focused practice. In other words, you want to master one topic before you move to the next. Have you been able to study in this way?
When learning about critical reasoning, for example, you want to be able to learn about all aspects of critical reasoning: strengthen and weaken the conclusion, resolve the paradox, find the conclusion, must be true, etc. Follow up your learning with targeted critical reasoning practice, so you can determine your specific weaknesses within that topic. You should do the same for sentence correction and reading comprehension.
To further improve your reading comprehension, I recommend reading publications such as the Economist, the New Yorker, Scientific American, and the Smithsonian, so you can get used to reading and analyzing long, sophisticated, well-written passages.
To truly master sentence correction, you must develop mastery of grammar rules (parallelism, subject/verb agreement, etc.) and accepted English usage. Concentrate on one topic at a time, such as modification, and practice with as many modification questions as you can find. Only after you feel confident with modification should you move to the next topic. In addition to your dedicated study, notice grammar and usage in your everyday life. Be aware of the things you habitually read, in terms of sentence structure, how phrases are worded, and whether pronouns are easy to understand, to name just a few important areas. Make sure you use proper grammar in your everyday writing as well. Have you put parallel ideas into parallel constructions? Do all of your pronouns refer appropriately to their antecedents? The more you reinforce your study with related activity outside of your study, the greater the likelihood you will master the topics, and have fun doing so!
Once you feel you have fully learned each verbal topic, begin taking practice exams to track your overall progress. You may consider taking the exams offered by GMAC, since those exams have an accurate scoring algorithm and contain retired questions from past GMAT exams.
Please keep me updated with your prep and, if you have any further questions, feel free to reach out to me directly.
Good luck!