i'd like to know when to use "i'd better" and is it i had better or i would better
I had better be good or I won't get any presents for Christmas.
I had better call John before he leaves the house.
I had better lie down for a while; I feel drowsy after the long drive.
You would not say "would better". Rather you would say "would be better"
It would be better if you didn't drink when you drive a car.
I would be better off if I saved my money instead of gambling it away at a casino.