As a modal verb, had better does not change its form for tense, person, etc. We use it to recommend action or give advice.
- You had better clear up the mess before mum returns.
- At your age, you had better have regular check-ups.
We can also use had better to issue warning or make suggestion about something bad that is likely to happen. We can use should/ought to to replace had better without affecting the meaning.
- You are coughing loudly.
- You had better see a doctor.
- You should/ought to see a doctor.
- I am overeating.
- I had better go on a diet.
- I should/ought to go on a diet.
- We think she had better not/should not/ought not to befriend him. He’s a drug addict.