I'm a university student studying at University of Leicester and I would aim my lessons at those in secondary school doing their GCSEs

I would first ask them what level they think they are currently working at in that subject and give them a practice paper to highlight topics they are struggling with. Then, I would cover the theory work behind it and at the end of the lesson, I would go through some example questions. After lesson is over I would give them some exercises related to the content we covered in the lesson and go through the answers in the next lesson.