You should do something = it is a good thing to do or the right thing to do.
You can use should to give advice or to give an opinion:
You look tired. You should go to bed.
The government should do more to reduce crime.
“Should we invite Susan to the party?” “Yes, I think you should.”
You shouldn’t do something = it isn’t a good thing to do:
You shouldn’t believe everything you read in the newspapers.
Should is not as strong as must or have to:
You should apologize. (= it would be a good thing to do)
You must apologize. / You have to apologize. (= you have no alternative)
We also use should when something is no right or not what we expect:
I wonder where Liz is. She should be here by now. (= she isn’t here yet, and this is not normal)
The price on this package is wrong. It should be $1.29, not $1.59.
That man ono the motorcycle should be wearing a helmet.
We also use should to say that we expect something to happen:
She’s been studying hard for the exam, so she should pass. (= I expect her to pass)
There are plenty of hotels in this city. It shouldn’t be had to find a place to stay. (= I don’t expect it to be hard)
You should have done something = you didn’t do it, but it would have been the right thing to do.
You missed a great party last night. You should have come.
Why didn’t you?
(= you didn’t come, but it would have been good to come)
I wonder why they’re so late. They should have been here an hour ago.
You shouldn’t have done something = you did it, but it was the wrong thing to do:
I feel sick. I shouldn’t have eaten so much. (I ate too much)
She shouldn’t have been listening to our conversation. It was private.
Compare should (do) and should have (done):
You look tired. You should go to bed now.
You went to bed very late last night. You should have gone to bed earlier.
Ought to …
You can use ought to instead of should. We say “ought to do” (with to):
Do you think I ought to apply for this job? (= Do you think I should apply?)
That’s a terrible things to say. You ought to be ashamed of yourself!
She’s been studying hard for the exam, so she ought to pass.