Look at these examples:
You should drink water every day. (recommendation)
He should study for the test tomorrow. (advice)
I should buy a gift for the teacher. (obligation)
They should be here by now. (expectation)
You can use any subject, place “should” after the subject but before the base verb.
Notice in the four examples, the underlined verbs are in their base forms. That is right! You don’t have to worry about any special endings on the verbs when you use them with should!
Here is the formula:
subject + should + base verb
We can change the subjects in the sentences and you will see that when we use should, the verb remains in the base form.