I am currently studying an M.Sc. ocean and climate physics and I studied physics in Barcelona. There I was a private tutor to high school students in mathematics and physics with good results. My way of working is to do exercises and resolve any doubts. I always tell the student to look at some exercises for the next class. It is not necessary to do them, for that there is the school, but only to read it and think a little, so the class is more productive.