If you have a sound base of preparation wherein you have covered certain important topics well, I suggest you start solving previous year questions year wise. Wake up every morning at 7 and solve a full question paper. Remember to time yourself as well. When you're done, take a break of 30 min and come back to check your answers. Spend the rest of the day practicing problems from the topics you answered incorrectly. If you do this process full justice, I have no doubt you'll score atleast 200 come April 8.
If you have done no preparation at all, I'm afraid 200 is a tall order. My suggestion would be to refer religiously to previous year questions. Covering every topic will be impossible, so choose some select topics and study them well.