Hi satishchaudharygmat,
To perform at a high level on SCs, you'll need a combination of knowledge (grammar and idiom rules), style ('meaning' of a sentence) and Tactics (knowing the common 'patterns' that the GMAT Tests, the common errors, etc.).
1) What practice materials have you used so far?
2) How have you scored on your practice CATs (including the Quant and Verbal Scaled Scores)?
3) What is your goal score?
4) When are you planning to take the GMAT?
GMAT assassins aren't born, they're made,
Rich