Using Should

One of the meanings of the modal auxiliary should is advisability:

--You should leave right now.
--They should fill out this form.

You can also express the same idea using either ought to or had better:

--You ought to leave right now.
(You had better leave....)

--They ought to fill out this form.
(They had better fill out....)

Should and ought to both mean that something is a good idea. Had better is usually stronger, implying a warning of bad consequences.

The negative of should is shouldn"t. Ought to is not usually used in the negative. Often you will hear people pronounce ought to as otta.