Susan gets very stressed, poor thing, because her parents have high expectations of her and she worries that she won't live up to them. She tries to study hard but if she gets distracted for an hour or so then she sees it as a failure and is very hard on herself.
Romilda believes that if you haven't learnt something by the time exams roll around, you're hardly going to be able to teach it to yourself. Therefore there's no point in wasting your time revising! If you know it, you know it. If not, big deal, who cares about failing an exam or two?
Draco also has high expectations from his father, but outwardly he doesn't let his worries show. He does, however, become more malicious and sarcastic around exams, and also more irritable. He wouldn't revise in the library because that would look like he's trying too hard, but he'll read over his notes in his dorm and perhaps get Pansy to test him on things.