We generally use HAD BETTER + bare infinitive to tell sb what they should do. It has more urgency than ‘should’.
You had better run or you’re going to miss your bus.
Your exam is in just a few days so you’d better start studying.
It’s getting late. I’d better go.
We often warn of the consequences if the advice is not taken.
You’d better phone your Dad right now, or he’ll be furious.
It’s really late. The children had better go to bed or they’ll be really tired for school.
You’d better not tell Sarah you had dinner with her ex. It would upset her.
HAD BETTER is also used to express a strong hope or even a threat.
The train had better get here soon or I’m going to be late for work. (strong hope)
There had better be some orange juice in the fridge. I’m so thirsty! (strong hope)
They had better not show any more adverts or I’m going to turn off the TV! (threat)
“I’ll pay you back tomorrow.” – “You’d better!*” (threat)
NB. For general situations use ‘should’ rather than ‘had better’.
For healthy teeth and gums we should brush our teeth twice a day.
Students shouldn’t use their phones during the class.
You really shouldn’t smoke Bryan, it’s so bad for you.
* = You’d better pay me back!