I do not have formal tutoring experience. However, after my A levels in 2011, I noticed my brother's E Math results for his Sec 3 End-of-Year examinations was only a D7. Having achieved A1 in E Math and A2 in A Math, I decided to give it a shot and try to help him. However, due to NS commitments, I could only guide him during the weekends.
During the holidays, I revised the Sec 3 topics with him. I looked through the exam paper and identified that he could not do specific topics. I had him do assessment book questions which targeted the topics he didn't understand. When he retried his exam paper at the end of the holidays, he managed to get 92 marks for the same paper he failed.