We use “had better” plus the infinitive without “to” to give advice. Although “had” is the past form of “have”, we use “had better” to give advice about the present or future.
You'd better tell her everything.
I'd better get back to work.
We'd better meet early.
The negative form is “had better not”.
You'd better not say anything.
I'd better not come.
We'd better not miss the start of his presentation.
We use “had better” to give advice about specific situations, not general ones. If you want to talk about general situations, you must use “should”.
You should brush your teeth before you go to bed.
I shouldn't listen to negative people.
He should dress more appropriately for the office.
When we give advice about specific situations, it is also possible to use “should”.
You shouldn't say anything.
I should get back to work.
We should meet early.
However, when we use “had better” there is a suggestion that if the advice is not followed, that something bad will happen.
You'd better do what I say or else you will get into trouble.
I'd better get back to work or my boss will be angry with me.
We'd better get to the airport by five or else we may miss the flight.