Expressing Advice

To express advice we use had better. Had better may be 

replaced by should and ought to.

For example :

You look sick today, you had better go to the doctor.

You look sick today, you should go to the doctor.

You had better stop smoking.

The negative form: 

Had better = had better not

For example:

It is getting sunny , i had better not close the window now.

Note : we use had better and had better not + verb in the infinity 

without "to"