From Michael Swan's Modern English usage - p 230.
We use had better to give strong advice, or to tell people what to do
(including ourselves)
- It's seven o'clock. I'd better put the meat in the oven.
Had better refers to the immediate future, but the form is always past
(have better is impossible). After had better we use the infinitive without to.
- It's late - you had better hurry up.
Had better is not used in polite requests.
Compare:
- Could you help me, if you've got time? (request)
- You'd better help me. lf you don't, there'll be trouble.
(order/threat)
Note that had better does not usually suggest that the action recommended
would be better than another one that is being considered - there is no idea of
comparison. The structure means 'It would be good to .. :, not 'It would be
better to .. .'.
Had is sometimes dropped in very informal speech.
- You better go now.
- I better try again later.