A.  Should—1)用來勸告他人該做什麼(或如何做); 2)也可詢問他人意見

1)  You should go ahead and finish the project now.

He shouldn’t leave school that early.

2)  Should I go to a counsellor?

How should I tackle this math problem?

B.   Ought to—同SHOULD1)肯定句用法;並不用在否決句或問句上)

e.g. She ought to carry a manual with her.

   They ought to buy the house now.

   I shouldn’t go there now.

C.  Had better (= ‘d better)—給予緊急的勸告

You’d better hurry or you’ll miss the train.

I’d better finish this paper by tomorrow, or I won’t get a grade for it.

D.  若我們自行給予他人意見,我們為禮貌起見,則會加maybe, perhaps, I think:

Maybe you ought to check out the place before you have a party there.

I think you should buy a small but a tasty ice cream cake for him.