Should and Must

Should

• We use should when we want to give an advise.
• In some cases it is mandatory, and you can use it if you want to give an order but in a polite way.

Must

• It means obligation.

Examples:

1. You should go to the doctor.
2. She must go to the principal's office right now. 

Practice

http://www.englishexercises.org/makeagame/viewgame.asp?id=1734

http://www.esl-lounge.com/student/grammar/2g18-should-shouldnt-exercise.php

http://www.englishexercises.org/makeagame/viewgame.asp?id=2786