Hiii nitesh....If you belong to Gen/Obc cat you should score75% or should be within top 20 percentile in your 12th exam and if you are from SC/ST, 65% in 12th exam will make you eligible for admission intoNIT/IIIT/CFTI or to take JEE adv subject to fulfilment of other requisite terms & condition.But one thing I would like to add that even if you don't score 75% or 65% as the case may be you can take JEE main and if you score decent marks you may try for:IIITHyd/IIITBhu/IIITRaipur/IIITDelhi/DTU/NSIT/Thapar University etc.There are also many institutes/universities which grant admission on the basis of JEEmain marks /AIR.