When a teacher is giving a lesson, take notes and if you don't understand something, raise your hand and ask questions. The more questions you ask, the smarter you'll get, believe it or not. Taking notes will help you think and help you understand what is being taught more.
The teachers expect you ask questions and form an impression of you from how willing you are to do so.
Concentrate on staying focused. Keep your eyes on the teacher, keep your ears open, and take notes.