1. SHOULD, OUGHT TO, HAD BETTER, MUST Modals verbs of advice

2. Should and ought to Should and ought to are basically the same in meaning however usage varies. Ought to is typically used to describe moral obligations and duty whereas should is typically used for general advice.  You ought to go to church every week.  We should study grammar more frequently.  He should take a shower or bath after coming home from the factory.  She ought to take better care of her children.

3. Should and ought to Shouldn't, or should not, is negative for either ought to or should.  You shouldn't eat a lot of junk food.  She shouldn't ignore her children.

4. Had better Had better is similar to should and ought to. It is different because typically it implies some sort of action or negative consequence if it is not followed. Note that even though “had” is past we are speaking in present or future (but not past).  He had better pay the rent.  You had better get your car fixed before the problem gets worse.  They had better go to the doctor since they were hurt by the explosion.

5. Had better Had better is contracted in spoken English with subject personal pronouns. 'pronoun'd better'  He'd better pay the rent.  You'd better get your car fixed before the problem gets worse.  They'd better go to the doctor since they were hurt by the explosion.

6. Had better The negative form of had better is had better not.  He'd better not forget to pay the rent.

7. Must Must is similar to should but it is stronger  You must stay in bed