Hi gk23sep91,
Here is some advice you can follow to improve your verbal skills. I’ll start with CR.
When studying Critical Reasoning, your first goal is to master the individual Critical Reasoning topics: Strengthen the Argument, Weaken the Argument, Resolve the Paradox, etc. As you learn about each Critical Reasoning question type, do focused practice, so that you can track your skill in answering each type of question. If, for example, you incorrectly answer a Weaken the Argument question, ask yourself why. Did you make a careless mistake? Did you not recognize the specific Critical Reasoning question type? Were you doing too much analysis in your head? Did you skip over a keyword in an answer choice? You must thoroughly analyze your mistakes and seek to turn weaknesses into strengths by focusing on the question types you dread seeing and the questions you take a long time to answer correctly. Follow a similar process for Reading Comprehension.
Sentence Correction, on the other hand, is a bit of a different animal compared to Reading Comprehension and Critical Reasoning. There are three aspects to getting correct answers to GMAT Sentence Correction questions: what you know, such as grammar rules, what you see, such as violations of grammar rules and the logic of sentence structure, and what you do, such as carefully considering each answer choice in the context of the non-underlined portion of the sentence. To drive up your Sentence Correction score, it is likely that you will have to work on all three of those aspects, and it is also likely that the reason that your Sentence Correction performance has not improved is that you have not been working on all three of those aspects. Let's discuss each of those aspects and how you can work on them.
Regarding what you know, to be successful in Sentence Correction, first and foremost, you MUST know your grammar rules.
Let's be clear, though: GMAT Sentence Correction is not really a test of knowledge of grammar rules. The reason for learning the grammar rules is so that you can determine what sentences convey and whether sentences are well-constructed. In fact, in many cases, incorrect answers to Sentence Correction questions are grammatically flawless. Thus, often your task is to use your knowledge of grammar rules to determine which answer choice creates the most logical sentence meaning and structure.
This determination of whether sentences are well-constructed and logical is the second aspect of finding correct answers to Sentence Correction questions, what you see. To develop this skill, you probably have to slow way down. You won't develop this skill by spending under two minutes per question. For a while, anyway, you have to spend time with each question, maybe even, say, ten or fifteen minutes on one question sometimes, analyzing every answer choice until you see the details that you have to see in order to choose the correct answer.
As you go through the answer choices, consider the meaning conveyed by each version of the sentence. Does the meaning make sense? Even if you can tell what the version is SUPPOSED to convey, does the version really convey that meaning? Is there a verb to go with the subject? Do all pronouns in the sentence clearly refer to nouns in the sentence? By slowing way down and looking for these details, you learn to see what you have to see in order to clearly understand which answer to a Sentence Correction question is correct.
There is only one correct answer to any Sentence Correction question, there are clear reasons why that choice is correct and the others are not, and those reasons are not that the correct version simply "sounds right." In fact, the correct version often sounds a little off at first. That correct answers may sound a little off is not surprising. If the correct answers were always the ones that sounded right, then most people most of the time would get Sentence Correction questions correct, without really knowing why the wrong answers were wrong and the correct answers were correct. So, you have to go beyond choosing what "sounds right" and learn to clearly see the logical reasons why one choice is better than all of the others.
As for the third aspect of getting Sentence Correction questions correct, what you do, the main thing that you have to do is be very careful. You have to make sure that you are truly considering the structures of sentences and the meanings conveyed rather than allowing yourself to be tricked into choosing trap answers that sound right but don't convey meanings that make sense. You also have to make sure that you put some real energy into finding the correct answers. Finding the correct answer to a Sentence Correction question may take bouncing from choice to choice repeatedly until you start to see the differences between the choices that make all choices wrong except for one. Often, when you first look at the choices in a Sentence Correction question, only one or two seem obviously incorrect. It may take time for you to see what you have to see. Getting the right answers takes a certain work ethic. You have to be determined to see the differences and to figure out the precise reasons that one choice is correct.
To improve what you do when you are answering Sentence Correction questions, seek to become aware of how you are going about answering them. For instance, are you being careful and looking for logic and details, or are you quickly eliminating choices that sound a little off, and then choosing the best of the rest? If you choose an incorrect answer, consider what you did that resulted in your arriving at that answer and what you could do differently in order to arrive at correct answers more consistently. Furthermore, see how many questions you can get correct in a row as you practice. If you break your streak by missing one, consider what you could have done differently that would have resulted in your extending your streak.
As with your Critical Reasoning and Reading Comprehension regimens, after learning a particular Sentence Correction topic, engage in focused practice with 30 questions or more that involve that topic. As your Sentence Correction skills improve, you’ll then want to practice with SC questions that test you on skills from multiple Sentence Correction topics.