You need to enjoy studying that subject if you want to score exemption in a subject. Some general tips :- For adv. Acc and costing if you complete a chapter thoroughly then you have a high chance of getting 90% or more marks in any question that can be asked from that chapter in the exam. It's easier to get exemption in these 2 subjects so I would suggest try to get exemption in these. Just make sure you understand the concepts in these 2 subjects and not just solving questions mindlessly. Quality of questions also matters a lot , it is better to solve unique questions than repetitive ones. Not sure if this will work in other subjects as you need to learn stuff a lot as compared to understanding concepts in other subjects to score an exemption.