You need to know exactly what it is that they need the help with. If the tuition is for exams etc, you need to know what syllabus they are following and what their strengths and weaknesses are. If the tuition is for adults you need to know their reasons for taking up the subject. I am MFL, I have taught young children who just wanted to learn for fun so there was no "serious" side to it, I have also taught for exams and most pupils need help with grammar etc, some may struggle with writing and some may struggle with reading etc. I have also taught adults who are moving abroad / need it for work etc. Get them to complete a basic self assessment where they give themselves a score of , say, 1- 10 on different topics. Others have mentioned having a cancellation policy. Maybe I have just been lucky but I have never been let down. You need to decide where the tuition will take place and if you are travelling you may want to charge extra for your time. Good luck.