It is difficult to say that Preliminary Examination is hard to crack or Main Examination is more difficult. Different candidates would have different opinion on this.
But, looking at the tough competition at Preliminary Examination level, one should be serious as without crossing this first hurdle, you cannot advance to next level.
Moreover, the syllabus for Preliminary Examination and recent question papers gives a feel that comparatively easier papers makes things more difficult for candidates.
So, the key to success at Prelims is ‘Practice’ as it helps you in building speed with accuracy.