If we want to say people what we think they should do we use different forms in written formal English and spoken informal English. In written English we use following expressions to make strong suggestion when we write in a formal style:
should + infinitive without to:
We should understand that apples are more useful than tomatoes.
You should do it better.
ought to + infinitive without to:
The teacher ought to do something with these rude students.
The goverment ought to do something about unemployment.
demand/insist/suggest + (that) + subject + should do something:
We are suggesting that the children garden should be rebuilt.
He is suggesting that the letter should be written again.
demand/insist/suggest + (that) + subject + present tense:
She insists that her money is transferred into another account.
He insists that book is written by him.
demand/insist/suggest + (that) + subject + subjunctive (the same form as infinitive):
The protesters demanded that the supermarket be closed.
The parents of the pupils demanded that the school be closed.
It is high time (that) + subject + past tenses:
It is high time the pupils got the books.
It is high time the council started to think about local businesses.
If we want to make weak, tentative suggestions when we talk to someone we know we use the following expressions in spoken English:
To make a slightly stronger suggestion, we use:
I think you should + infinitive without to:
I think you should go out with your friends tonight.
I think you should buy this dress.
I think you ought to + infinitive without to:
I think you ought to give away your old scholl books.
I think you ought to call one more time.
We use following expressions to criticise, reproach or advise somebody in a strong way. These expressions are often used by a person in authority.
It's about time + subject + past tense:
It's about time they got down to work.
It's about time you wrote down the task.
I'd (=I would) rather + subject + past tense:
I'd rather you didn't do that.
I'd rather you didn't buy this dress.
You'd (=You had) better + infinitive without to:
You had better start reading the book.
You had better hurry up or you will be late.