dear sonu,

see jee main is a all India entrance test for engineering and this exam is the gate way of many reputed engineering colleges in India. so I think you have the idea how the question level is going to be. and for competitive exam there is no suggestion can be made , as this is a mcq base exam, question can be ask from any where. I dont know what is your 10+2 exam preparation , if your 10+2 exam preparation is good then you may answer atleat 40% question. but if your 12th exam preparation is also not good please have focused on it. because 12th exam marks is very essential for your future career prospect. and you may appear in jee main on next year but you cannot get another chance for scoring good in  10+2 exam . hope you may understand.