You must wear school uniform
You must have your diary with you
You must take all your books and exercise books
You must be disciplined at your classes
You must listen to your teacher
You must be precise at the lessons
You mustn't talk at the lessons
You mustn't ague with your class-mates
You mustn't loaf at school

The first to study hard. The second  school should be your top priority. 
You should be ready with your homework, and be active at your lessons, and be always at the top of your doing. 
The third is to have a good behavior. 
you must not be late at your lessons,and turn off your mobile phone, and bring everything that you need in this class (for instance, book, pens, and paper). 
Do not be lazy