I’m very tired, but I need to go to work. What should I do?

You shouldn’t go to work. It isn’t a good idea. Instead, go to the doctor.
You shouldn’t drink fizzy drinks, you should drink fruit juice.
You should go to work, but you should ask your boss for a day off.
Advanced Grammar Exercises
Elementary Grammar Exercises A1
Upper-Intermediate Grammar Exercises
Intermediate Grammar Exercises