We use must / mustn't...
Obligation / prohibition. Rules, laws (no choice).
We use should / shouldn't...
Advice / Opinion. Recomendation.
Eat fruit and vegetables.
You should eat fruit and vegetables.
Take pictures.
You mustn't take pictures.
Wash your hands before eating.
You should wash your hands before eating.
Watch TV from very close.
You shouldn't watch TV from very close.
Shower before entering the swimming pool.
You must shower before entering the swimming pool.
Wear a uniform in Hogwarts.
You must wear a uniform in Hogwarts.
Wear shinpads in football.
You must wear shinpads in football.
Touch the oven when it is hot.
You shouldn't touch the oven when it is hot.
Play with your food.
You shouldn't play with your food.
Keep your bedroom tidy.
You should keep your bedroom tidy.
Touch the paintings in the museum.
You mustn't touch the paintings in the museum.
Step on the grass.
You mustn't step on the grass.
Shout at your friends.
You shouldn't shout at your friends.
Wear a coat if it is cold outside.
You should wear a coat if it is cold outside.
