Hi Sachin,
As the son of an English professor, I can't resist an invitation to correct someone's grammar!
One issue is how you work with certain verbs. You don't "refer" a book, you "refer to" it. So you would ask "To which book should I refer?" or, less formally, "Which book should I refer to?"
On a similar note, we don't "suggest you," we "suggest" or "suggest to you." So the easiest way to rewrite your request would be "Kindly suggest how to improve my score in Verbal." Grammatically, then, "suggest the mistakes" is correct, but we aren't really suggesting them, so it would be better to ask us to "point out the mistakes."
In terms of individual words (diction/spelling), there are a few issues:
*The contraction for "it is" is "it's." "Its" is possessive, as in "A lizard can release its tail."
*quiet = not loud. You want "quite."
*"Query" has one r.
Idioms: No blatant errors here, but be cautious about your use of "with" and "without" study/practice. "With practice" is an adverbial modifier--it modifies an action, not a noun. So a test can't be "with practice"--only your performance on the test can be.
*Also, a regional note: In the US, we say that we take a test, rather than give one. (If I say I gave a test, that means I administered the test to someone else.) However, this is not an error--it's just a regional variation--and everyone here on gmatclub will understand you.
Thanks for the invitation! I almost didn't take it up since you are just starting out and I don't want to discourage you! So . . . I hope you my advice encouraging.