Hi Imran,
I am both a language student and a language teacher with over 6 years of experience (mostly not online). I'm assuming that you are teaching online lessons. I think this varies a lot because these lessons are so individualized. I haven't seen any numbers, but by looking at reviews, it is common for students to do a package with a teacher on iTalki and then move on. Some teachers have students for many, many sessions. I would say the most important thing is to try to form a connection with your students. I've had teachers on iTalki that are technically very good, qualified teachers, but bring nothing of their personality to the lesson. Some students might like that, but I feel it is a bit robotic--like working with a very sophisticated computer program. If you form a good connection with your students, they will feel comfortable telling you what you could do better for them.
Of course, that is just my opinion. Some students like the more impersonal approach. Those students will find those teachers.
Kevin