Should is used to express mild obligation and advice.
SHOULD + PRESENT
- To give advice, suggestion, recommendation. It means we say the right/correct thing to do. Example: You are too fat, you should go on diet.
- To express obligation. But it is not as strong as "must". Example: You should pay attention to the teacher's explanation.
- To express situation likely in the present. Example: Andi should be at home, meet him now!
- To predict situation in the future. Example: You have checked in the doctor. You should be fine tomorrow.
Note: Should not (Shouldn't) To advise someone not to do something because it is bad/wrong. Example: You should not cheat in the exam.
(+) Subject + Should + Verb 1
(-) Subject + should + not + Verb 1
(?) Should + Subject + Verb 1 + ?
(+) I should go.
(-) They should not litter here.