According to my friends from Delhi University, it is not easy to maintain 67% attendance. You will have to attend classes regularly and it also depends on your timetable. If you have 7 lectures per week for a specific subject, you have to attend at least 4, in order to achieve 67% attendance. Also, the classes can get canceled for fests/events/protests, etc. So, don’t bunk classes frequently. Especially if you are in any kind of society. In that case, even after as many classes as you can, you won’t have an attendance percentage above 70-75%. 

If you are not in any kind of society, it’s better to attend more than half of the lectures each week.