Had better

Had better refers to the immediate future. It is followed by an infinitive without to. It is a strong advice. We use it to tell people what to do.

§  You had better consult a doctor.

§  You had better apologize. 

§  We had better hurry up. We are already late. 

Had better sometimes suggests a threat and is not used in polite requests.

§  You had better tell them soon. If you don't, there will be trouble. 

§  You had better mend your ways. 

To make negative forms, we put not between had better and infinitive.

§  You had better not irritate him. 

Should, ought to, must

Should and ought have similar meanings. They are both used to talk about obligation, and to give advice or instructions.

·         We should respect our parents.

·         We ought to respect our parents.

·         You should stop smoking.

·         You ought to stop smoking.

Must is stronger than should and ought.

§  You must stop smoking. (A command.)

§  You should/ought to stop smoking. (A piece of advice.)

Must expresses certainty. Should/ought to expresses probability.

§  He must be home now. (It is certain.) 

§  He should be home now. (It is probable.)