Should and were to can also be used in the if-clauseA group of related words containing a subject and a verb. of third conditional sentences. To express that the sentence refers to past, however, a perfectThe aspect expressing completion. E.g.: He’s finished university. infinitive is used after them. Note that this usage (like the situation it expresses) is not very common.

SHOULD

Should can be used after in case to emphasisSpecial importance or attention given to something. E.g.: All I wanna do is have some fun.e unlikelihood. This use is rather formalNot belonging to colloquial or everyday speech; official. E.g.: I demand that Mr Smith call the person on whom the committee has decided. or may even sound archaic to some speakers.

SHOULD

Should + perfectThe aspect expressing completion. E.g.: He’s finished university. infinitive can be used to emphasisSpecial importance or attention given to something. E.g.: All I wanna do is have some fun.e unlikelihood in the past. This use is rather formalNot belonging to colloquial or everyday speech; official. E.g.: I demand that Mr Smith call the person on whom the committee has decided. or may even sound archaic to some speakers.

In second conditional, the past subjunctive form of be to is used to express that a condition is less likely.

This structureThe way in which the parts of a sentence, clause or expression are arranged. E.g.: make somebody + infinitive in "The teacher made me rewrite the composition." can express arrangements and orders.

The concert is to begin at 6. (arrangement)
You are to tidy your room before your friends get here. (order)

This structureThe way in which the parts of a sentence, clause or expression are arranged. E.g.: make somebody + infinitive in "The teacher made me rewrite the composition." is used for formalNot belonging to colloquial or everyday speech; official. E.g.: I demand that Mr Smith call the person on whom the committee has decided., official arrangements.

All students are to take the Academic English Exam at the end of the first year.
"Clone expert is to clone human embryos".
"The Prime Minister is to visit Pakistan next month".

If + subjectThe person or thing that performs the action of a verb or that is described by a verb. E.g.: Andy has never been to Brunei. ("Andy") + auxiliaryA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") can be replaced in formalNot belonging to colloquial or everyday speech; official. E.g.: I demand that Mr Smith call the person on whom the committee has decided. English, or for dramatic effect, by the inversionA structure in which a verb or an auxiliary precedes the subject. E.g.: "Here comes the sun." of the auxiliary and the subject, with the if omitted.