Do and make are such flexible verbs that when I think of an explanation, I can also think of something opposite. Without looking at the exercise, usually we say make *something* worse / make *something* better. For example, I can make the situation better/worse. You'll make it worse than it is now. "Do better/worse" can refer to a performance. For example, today I ran a mile in ten minutes. Tomorrow, I'll do better. You barely passed the exam, but I am sure you can do better next time. Edit: After looking at the exercise, I'd say I agree with you. They are difficult for a learner. There are no obvious rules that I can see.