Should and Should Have
We use "should" as modal verb to give advice and express obligation.
Formula: Subject + should + 1st form of the verb + object
You should drive carefully all the time. (simple sentence)
She should not / shouldn't drink vine this much. It's not good for her health. (Negative sentence)
Formula: Subject + should have + 3rd form of the verb + object
We should have discussed it before. We may have had better solution. (simple sentence)
They shouldn't have behaved like that otherwise mother wouldn't have been annoyed. (Negative)
We should be in America by the end of this month. (simple sentence)
Ibrahim shouldn't go with Sarah to the party. (Negative sentence)
You should switch off the light when you leave the room. (simple sentence)
We should stand against the government's negative step.
Note: We don't commonly use negative sentence for obligation.
We can also use "Be Supposed to" in place of should with the meaning.
Be Supposed to
I am not supposed to leave the class before taking lecture.
You are supposed to be with your mother during her illness.
Ibrahim and Sarah were supposed to compromise.
You were supposed to phone me.
"Ought To" is used quite similarly to "Should"
We ought to fight against cancer.
See also Ought To