Hi Saumya,
In general terms, the correct answer to a Strengthen CR will provide some type of additional information that affirms/confirms the ideas in the prompt. In many cases, the correct answer will involve some new 'data' that confirms the logic the author is using. In rarer cases, the correct answer will 'remove' alternative possibilities/explanations from the discussion (which, by extension, strengthens the validity of the author's logic).
1) Are 'strengthen' questions the only types of CR prompt that you're having trouble with? How well do you do on 'weaken' questions or other CR question types?
GMAT assassins aren't born, they're made,
Rich