RULE # 1: RULE # 1 When Had becomes Unreal Past; the meaning becomes Present or Future: I had better ring him at once/ tomorrow. (This would be a good thing to do/ the best thing to do.) You had better consult a doctor. (This would be a good thing to do/ the best thing to do.) I had better inform him as soon as soon possible. (This would be a good thing to do/ the best thing to do.)
RULE # 2: RULE # 2 The Negative is formed with Not after Better : You had better not miss the last bus. (It would be unwise to miss it, or I advise/ warn you not to miss it.) Had here is usually after Pronouns and in contracted speech is sometimes so Unstressed as to be almost inaudible.
RULE # 3: RULE # 3 Had Better is not normally used in the ordinary Interrogative, but is sometimes used in the Negative Interrogative as an advice form: Hadn’t you better ask him first? Hadn’t she better seek permission? Hadn’t they better inform us first? Hadn’t he better take leave?
RULE # 4: RULE # 4 You Had Better is very useful Advice form: You had better fly. (It would be best for you to fly, or I advise you to fly.) You had better take exam. (I advise you to take exam.) They had better practise hard. (I advise them to practise hard.)
RULE # 5: RULE # 5 In Indirect Speech Had Better with 1st or 3rd person remains unchanged; Had Better with the 2nd person can remain unchanged or be reported by Advise+Object+Infinitive: He said, ‘I’d better hurry’= He said (that) he’d better hurry. He said, ‘Ann had better hurry’= He said (that) Ann had better hurry. He said, ‘You’d better hurry’= He said (that) I’d better hurry or He advised me to hurry.