The most important thing for prelims is attentiveness and good judgment. Both come from a deep and intelligent preparation. Refer to some good guide like Unique or Spectrum. Make sure that you start solving previous years' papers as soon as you start you preparation. Due to negative marking you have to be very judicious before attempting your questions. Even now some kind of intelligent guess should work, but dont touch any question about which you are sure you dont know anything. This habit can be developed only after exercising with as many practice tests as possible.