Knowing your students is very important in a language class and you, as a teacher have to do it in the first day. But what kind of information you need to know ? I am talking here in terms of Bangla/Bengali language which I have been teaching for 25 years to non-nantive speakers.
You can teach in a regular classroom in an University, or in a tutoring session outside of academia. You can have one student or several students in your class. But in your first interaction with students, you have to figure out their language backgrounds and goals. Whatever you teach, the success lies in understanding your students.
The questions you need to address are like these, is it the first time, your student X is learning a language besides English ? If the answer is 'yes' , then you have to think about all the possible challanges, she may have, in terms of cultue, language structure, pronunciation, writing etc. ( let's guess that X is a female student so I can use 'she' for her)
If X has learned some European languages,she will have some idea how to process a second language in her mind, what to expect from a class etc. You will also know what to expect from her. For example, if I have a student who knows Spanish, I will immediately guess that that student is familiar with dental sounds and other irregularities of language structures.
There is a possibility that X knows some other South Asian languages, like Hindi or Tamil. In that case, you will face different kind of blessings and challanges as a teacher. If X knows Hindi, she will catch up Bangla very quickly. But, Hindi has left some prints in her mind, like usage of 'to be' verb and you have to help X unlearn the pronunciation of sounds of the alphabets.
Take a mental note or real note of your students' background but do not forget to ask about their goals. Ask your students why are they learning Bangla ? Some of your students will just want to talk to their family and friends. Some want to learn Bangla for their research purposes. So, this means some give emphasis on speaking and listening, somewant to read texts. You will also have some students who are not sure what they will do with Bangla in future. Everything is okay, value every background and every goal and then start your lesson.