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.

Examples of Using Should

• My bank and previous charge accounts are all abroad. What should I do?
• We should have approval within ten days. Where shall we mail your card?