i want to do mba from IIMs and want to give cat in 2013 but without work experience i scored 68% in 12th and 86% in 10th so what to do

Try securing above 99 percentile overall with sectionals above 95 percentile each. This will help you get a seat in IIMs and compensate for low acads in 12th. Having experience will only help you to the extent of deciding the specialization tio opt for i.e whether to go for finance/HR/operations/mar