F. 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. (e.g. You look tired. You should go to bed.)
a. often use with I think/ I don’t think/ Do you think ~? (e.g. I think the government should do more to reduce crime.)
b. You shouldn’t do something + it isn’t a good thing to do. (e.g. You shouldn’t believe everything you read in the newspapers.)
c. ‘Should’ is not as strong as ‘must‘ or ‘have to’. (e.g. You should apologise. (= it would be a good things to do))

F1. can use ‘should‘ when something is not right or what you expect. (e.g. I wonder where Tina is. She should be here by now. (= she isn’t here yet, and this is not normal))
a. also use ‘should’ to say that we expect something to happen. (e.g. She’s been studying hard for the exam, so she should pass. (= I expect her to pass))

F2. You should have done something = You didn’t do it, but it would have been the right thing to do. (e.g. 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))
a. You shouldn’t have done something = you did it, but it was the wrong thing to do. (e.g. I’m feeling sick. I shouldn’t have eaten so much. (= I ate too much))
b. Compare: You look tired. You should go to bed now. vs. You went to bed very late last night. You should have gone to bed earlier.

F3. can use ‘ought to’ instead of ‘should‘ in the sentences. We say ought to do (with to) (e.g. Do you think I ought to apply for this job? (= Do you think I should apply ~ ?))

F4. can use ‘should‘ after a number of verbs: demand, insist, propose, recommend, suggest. (e.g. They insisted that we should have dinner with them.)
a. also say ‘It’s important/ vital/ necessary/ essential that ~ should ~‘. (e.g. It’s essential that everyone should be here on time.)
b. can leave out ‘should’ in E and E1 sentences. (e.g. It’s essential that everyone be here on time. (= that everyone should be here))
c. This form (be/ do/ have/ apologise etc.) is sometimes called the subjunctive. It is the same as the infinitive (without to) can use normal present and past tenses. (e.g. It’s essential that everyone is here on time. I demanded that he apologised.)
d. After suggest, you cannot use to ~ (‘to do/ to buy’ etc.) (e.g. What do you suggest we should do? or What do you suggest we do? (but not What do you suggest us to do? Ann suggested that I (should) buy a car. or Ann suggested that I bought a car. (but not Ann suggested me to buy))
e. can also use ‘~ing’ after suggest. (e.g. What do you suggest doing?)

F5. can use ‘should’ after a number of adjectives, especially: strange, odd, funny, typical, natural, interesting, surprised, surprising. (e.g. It’s strange that he should be late. He’s usually on time)

F6. can say ‘If something should happen ~’. (e.g. If Tom should phone while I’m out, tell him I’ll call him back later.)
a. can also begin with should. (e.g. Should Tom phone, tell him I’ll call him back later)

F7. can use I should ~ / I shouldn’t ~ to give somebody advice. (e.g. Shall I leave now? No, I should wait a bit longer. Here, I should wait = I would wait if I were you, I advise you to wait.)