Your students not only speak a different native language, they also have acquired a different system of nonverbal behavior, through which much of communication takes place. As you can imagine, there is plenty of room here for you to misunderstand them and for them to misunderstand you, even if your English proficiency is very high. Observe the nonverbal behavior of American GSIs and their students, taking note of such things as their clothes, the distance between them, their movements, the signals they give that they are listening, and the expressions they use to show agreement or disagreement, interest or boredom, and understanding or the lack of it. To the extent that you can learn and use the nonverbal behaviors of Americans, your mutual understanding will be enhanced. If you feel uncomfortable with some aspect of the American nonverbal communication system, explain your own system to your students so they will understand you better.
Every new teacher faces a great challenge.
For you, the task of teaching includes reaching across different cultural values and assumptions, different educational systems, different native languages and non-verbal communication systems. Thus, the challenge is greater, but so is the opportunity. As an IGSI, you have the chance to develop a truly sophisticated command of English, to which you have already devoted a great deal of effort. You also have the opportunity to get inside an important part of American culture, the educational system, to understand and affect it by your contributions. Furthermore, you are invited to enter into a meaningful, cooperative relationship with your students, giving both them and yourself a memorable, enriching experience.