I have worked as tutor (outside italki - not for languages) and of course you CAN use books, etc..

Italki, as far as I understand, just makes sure that people, who want to become a "teacher" have a formal qualification in that field. That can be very helpful for students, who need to prepare for exams or need to have grammar explained in detail etc. Those teachers then should have the material to explain and practise this.

I find that a good tutor is rather a person, who helps where it is needed and not someone, who gives structured lessons.

For example: I prefer to learn the (Spanish) grammar out of a (German) textbook. Mostly it is clear (in theory at least). What I then need is someone to practise it with: Repeating the lists of irregular verbs, making short sentences with the words I have learnt etc.

What I have experienced is that many tutors and teachers overdo it: Each time I make a mistake (which is natural as I am learning), they (want to) start and spend time on explaining grammar. It took me a longer time (and some money for trying out several tutors) to find someone, who simply helps me, where I need it at the moment. And if it is a boring repeating of short sentences for 60 mins, then it is fine with her.

Through when the student doesn't have specific requests it might be good to have some material (text, picture) to start a discussion. Otherwise you tend to talk about the same topic over and over again (personal interests of either of you). 

My personal opinion.

As a learner, I would like to register my opinions about English teaching. 

A wide range of English materials is absolutely necessary for English learner to learn English with effectiveness and efficiency, so that means if you can make good English materials to facilitate English learning, you must be able to engage some group of people who are interested in your English teaching. 

I personally believe videos and audio materials are more relevant than texts or books despite they are also important for an advanced learner,. Certainly, most of the English learners are worse in speaking and writing (productive side), especially young learners, in other words, young people are probably more interested in good English learning materials in speaking and listening. 

In terms of advanced learning, I consider reading and writing are more important than speaking and listening. But no matter what, I cannot stress more about the importance of "INTERACTION". I am convinced that a good teacher is the one who is good at building a good atmosphere and environment to develop "interaction" in any case. 

Personal perspective

I'm new guy to this platform ,very glad to know promising tutor like you.  

I think "before class text"(some text we can read for build communication context before the class)  will be very helpful.