1. You shouldn't be so serious all the time. You ought to join a club or something, and you will have more friends.
2. I think you shouldn't spend so much on CDs. You ought to save some money, so you'll afford to go the the cinema more often.
3. You shouldn't try to do so much sport. You ought to focus on one sport, so you'll be good at it.
4. You shouldn't wash your hair so often. You ought to leave it for a few days between washes, and it would become bearable.
