Hey Rosie, it looks like you are new to italki and you are searching for new students.
It depends on the language. A lot of students of English from developing countries need to speak English to land higher paying jobs (i.e. - in Mexico, Colombia, Brazil, etc if a salesperson speaks English in addition to Spanish or Portuguese, their salaries can go up by 50%+). Others who are well-off financially learn English to communicate better when they travel in Europe or other countries. They understand that in a hostel at their next destination, if a group of people from 5-6 different countries gather to socialize, they will almost always use English as their bridge language.
Those from developed countries often learn a new language for fun (more common), or for a spouse (maybe a guy has a girlfriend from a different country and he wants to impress her parents, and this is not very common)
If you want new students, just show that you are an outgoing, non-judgmental person who listens and has interesting stories to share. Most students don't care about grammar; they just want a great conversation (a teacher who is like a friend). A small minority of students enjoy grammar.