Discipline ——纪律 “self discipline ”——自我约束或者自律 “ mental focus”——精神集中 So "self discipline and mental focus"means "约束自己并且集中精神“ It`s used to say to students to manage classroom.

When "Discipline" is used as a noun and means the practice of making people obey rules, it is always translated into "纪律", and when it means the quality of being able to behave and work in a controlled way, usually translated into "律", such as "self discipline"——''自律".

紀律

discipline in this context could be translated into "纪律". self discipline means “自我纪律”，but is usually expressed as "自律“。