Zarun:
I think it's not an appropriate thread to talk about improving one's English. May be other users who are following this thread are looking for motivation, and they won't like to read something regarding English.
Anyway, I'm myself not an authority on this subject but I think what made me pass these two papers was my childhood habit of reading.
Work on basic grammar, the grammar we were taught in high school would I suffice. Mistakes can be overlooked but not BLUNDERS. So learn basic English grammar so that you can avoid mistakes like: " I want to GIVE CSS exam" we don't give, we take exams. The problem is that we have a habit of thinking in Urdu -- mein CSS ka exam DEYNA Chatha hoon" and then translate it.
Alright comrades, I know I'm dwelling on trivialities.
Zarun bro, just visit the thread labelled ENGLISH and post your queries. There you'll find advice from gurus, not naieves like me.