Should have – various usages.

1.  To denote something that was more desirable than what was available .  Or a situation where one was doing something which was not the proper/appropriate thing compared to what they should have been doing.

• That is not the kind of job you should have been doing.(i.e the speaker thinks more appropriate kind of job was something else instead of what he was doing)
• He was sitting idle while he should have been studying his lessons.  (i.e the speaker thinks that the examination was very close and normally a student should have been busy studying instead of sitting idle)
• I wonder where Jithu was.  He should have been there by then for his tabala performance.(i.e Jithu was not there as planned/expected)

2.  Should have -ed ( refers to past obligation or duty left undone)

• You should have helped him. (i.e He was a deserving person but you didn’t help him)
• Your application will not be considered.  You should have submitted it by December 31st.

3.  ‘ You should’ and ‘ You should have’ are used when you are telling someone that something is or was very surprising, unusual, amusing etc and that is a pity  they didn’t witness it.

• You should hear the way she talks to me.
• You should have seen it!

4.  To make a present supposition about the past.

• We took the wrong road an hour ago.  According to the map, the road going to east should have been our way.
• What he said should have been correct. ( Now I presume it was correct from the circumstances that warrant my supposition)

5.  The suggestive use of ‘ Should have (done) ‘

• I am surprised that you should have felt upset. ( suggests that I am surprised at the fact that you were upset)
• I can’t understand why you should have said that .( i.e You said something which one cannot normally or reasonably agree with)