As you probably know, there are thousands of people around the world who teach English without having a very good level themselves. Although this is not the ideal situation it is the reality. It's probable that you also learnt English from a non-native speaker but you can get better, much better . This will also help your students to learn English well.
Both you and your students need to have regular contact with a "good" model of the English language. A baby needs as much as 3,000 hours contact with its own language before it can speak it! It then needs quite a few more years before it can speak it well, and then even more time before it can read and write in its own language.
What does this mean? That you have to programme regular time for reading and listening to English. It's much better to listen to a short dialogue 3 or 4 times than to watch a complete film in English just once. You should also encourage your students to do the same. Good luck