you should do something = it is a good thing to do or the right thing to do

should. 用来提出建议、劝告。
you look tried , you should go to bed .
The goverment should do more to help homeless people.
should we invite Susan to the party ? yes , I think we should.

i think / i don't think / Do you think ... ? 后面的从句中常用should.
i think the goverment should do more to help homeless people.
i don't think you should work so hard.
do you think i should apply for this job ? yes , i think you should.

you shouldn't do something = it isn't good thing to do.
you shouldn't believe everyhing you read in the newspaper .

should 没用must那么肯定。

 you should apologise. （ 这是应该做的事）
you must  apologise  (你已经没有其他的选择了）

should 还用来表示某事不对头 或者 像我们想象的那样。

i wonder where Lis is . she should be here by now.
The price on this packet is worng . it should be $1.5 not $1.2.
(1．36→one point three six）
Those boys shouldn't be playing football at this time . they should be at school.

should 用来表示希望做或发生的事。

she's been studying hard for the exam . so she should pass.

there are plenty of hotels in the town . it shouldn't be difficult to find somewhere to stay..

you should have done something = you didn't do it but it would have been the right thing to do.

it was a great party last night . you should have come . why didn't you?
i'm feeling sick, i shouldn't have eaten so much chocolate.
i wonder why they're so late. they should have been here an hour ago.
she shouldn't have been listening to our coversation . it was private.

请比较 should (do ) 与 should have done .

you look so tired . you should go to bed now.
you went to bed very late last night . you should  have gone to bed earier.

ought to ...

注意 ought to do .. 要加do.

do you think i ought to apply for this job ?

= (do you think i shoudld apply for this job?)

jack ought not to go to bed so late . = (jack shouldn't go )
it was a great party last night . you ought to have come.
she's been studying hard for the exam . so she ought to pass.

should (2)

shou