We use should, ought to, and had better with an infinitive (e.g. go, eat, hurry):

We use both should and ought to to ask for or to give advice, to say what is the correct or best thing to do:

• A: I’ve got toothache. What should I do? (= What is the best thing for me to do?)
• B: You should go to the dentist’s. (= The best thing for you to do is to go to the dentist’s.)

When we are talking about a duty or a law, we usually use ought to:

• A: I saw a car accident. What should I do?
• B: You ought to report it to the police. (= It is a person’s duty to report it.)

On the other hand, when we are giving a personal opinion, we use should:

• B: I think you should forget about it.

We use should much more than ought to in negatives and questions:

• I shouldn’t (or I ought not to go.)
• Should I go? (or Ought I to go?)

We can also use had better to give advice, to say what is the best thing to do:

• The train is going to leave now. You had (or You’d) better get on it.
• I’ve got to wake up at 4 am. I had (or I’d) better go to bed early.
• I had (or I’d) better go to the dentist’s. I’ve got toothache.

Note that had is a past form, but it does not refer to past time here; we use it to talk about present or future time.

We only use had better to give advice about a specific thing or situation; when we give general advice, we use should or ought to:

• When people have a problem with their health, they should go to a doctor. (not … they had better go …)

The negative is had better not:

• I’d better not drink any more coffee today. I have to wake up early tomorrow.