We use should when something is a good idea; it is a good thing to do.
To be polite, you can say, I think you should…
I think you shouldn’t eat so much.
I think you should talk to her about it.
I think you should reconsider our offer.
I don’t think he should attend the conference.
Ought to is the same as should, but generally used only in positive sentences:
I think you ought to eat less.
Perhaps you ought to talk to her about it.
You ought to think about reconsidering.
Expectation and probability
We can also use should and ought to to talk about something we
expect will happen, or something that is likely to happen:
Where’s Giovanni? He should be here by now.
My train is late, but I should arrive around 10pmg.
I’ve studied hard, so I ought to pass the exam.