• We usually use had better to give advice or warning or make a suggestion about something bad that is likely to happen.

EXAMPLE: You are coughing loudly. You had better see a doctor.
EXAMPLE: I am overeating. I had better go on a diet.
EXAMPLE: We think she had better not befriend him. He is a drug addict.

• Had better can be replaced by should/ought to and retain the meaning.

EXAMPLE: You are coughing loudly. You should/ought to see a doctor.
EXAMPLE: I am overeating. I should/ought to go on a diet.
EXAMPLE: We think she should/ought to befriend him. He is a drug addict.