For example, "You had better clean your room!"
This is a phrase that might be spoken from a parent to a child, and heavily implies that there will be consequences if the action isn't performed. You can also say something like "The package better have been delivered." which means that expectations were set and you are depending on it for some reason or other, and you are going to be angry/upset if your expectations aren't met.
The closest I can think of would be some use of either müssen or sollen, but they don't really convey the same meaning as the above English phrase. I suppose it might be done with one of those fancy particles, but my grasp of when to use those is loose at best.
My best guess is something like, "Du musst bloß dein Schlafzimmer putzen!"