Must and Should

Should is used to give advice, to make recomendations or to talk about what we think is right or wrong.
form
should + infinitive without to
Ex. John should be more careful. He won´t be so lucky next time.
You should eat mor slowly.
I should take some exercise if I wont to fell fine.

Negative form
You shouldn`t work so much
You shoudn`t touch anything electrical if you are in bath.

Must is used in affirmative statements to express obligation or strong need in the present.
form
Must + infinitive without to
Ex. affirmative form:
You must get a working permit if you want to get a good job here in the USA.
I must worry about the exam if I were you. You have worked really hard.

Negative form:
You mustn`t drink so much. It`s not good for your health.
You mutsn`t come to school on time.