1）should和ought to意思相近，表示“应该做某事”。
例句
a. You should do as you are told.
b. Drivers should / ought to obey the speed limit.
2）had better常用于口语中，后面接动词原形，否定用had better not，含有警告或警示的意味，如：
We had better study harder, or we’ll probably fail in the exam.
我们最好学习努力点儿，否则可能会考试不及格。