Should – various usages :

1.  To give advice, opinion etc

• You look tired.  You should go to bed.
• You should seek the advice of the Principal before taking an action.
• Should we hire a taxi or go by bus?

2 .We use ‘should’ with”  I think/I don’t think/Do you think? “etc

• I think you should consult a doctor.
• I don’t think you should submit the resignation now.
• A:  Do you think I should apply for this job?
• B:  Yes, I think you should.

3.  Should/should be doing :  This is to express a wish about what you would like to be doing rather than what you are actually doing.

• That is not the kind of job he should be doing.( actually he is doing some job which the speaker thinks not fit for him, the speaker thinks some different type of job would be apt for him.)
• He is sitting idle while he should be studying his lessons.( i.e For a student, this is not the time to sit idle, but study hard because the exam is close)
• I wonder where Jithu is.  He should be here by now for his tabala performance.( i.e he isn’t here yet and his absence is viewed with disapproval)

4.  I should like = I want ( formal or polite way)

• I should like to ask you a question.
• I should like to know when I can meet the principal.
• I should like to get your valuable advice.

5.  We use ‘SHOULD’ to say that we expect something to happen.

• She has been studying hard for the exam, so she should pass.(i.e I expect her to pass)
• It shouldn’t be difficult for you find somewhere to stay tonight.(i.e I don’t expect that it will be difficult……….)

6.’ SHOULD’ is not as strong as ‘MUST’ when it refers to duty or obligation.

• You should apologise .(i.e it would be a good thing to do)
• You must apologise.( you have no alternative but to apologise)

7.  If………Should

• I have left the washing outside.  If it should rain , can you bring it in?(i.e here the chance of rain is very remote, but to be on the safer side the speaker requests for help.)
• If he should phone while I am out, tell him I will phone him back later.( i.e the chances of his phone call is remote/unlikely)

The ‘suggestive’ use of ‘SHOULD’.

• I am surprised that you should feel upset. ( suggests that I am surprised by the idea of your being upset now)
• I can’t understand why she should say that.( i.e I can’t understand what makes her say it now.)