what is important to learn second language

I teach basic English to Japanese old people on online. What I always keep in mind is to make fun lessons for students. Our lessons doesn't have system which to ask for a certain person, But, some students request my lesson. every student doesn't tend to have fun lesson. I have to figure out student personality to satisfy my lessons while they introduce themself about 10 min. I always try to organize best lesson for student. I think it is easy to figure out students strengths and weaknesses, Because Japanese is my mother language.